Video processing using local illumination compensation

ABSTRACT

A video processing method is provided to include: determining, based on a position rule, whether a local illumination compensation (LIC) tool is enabled for a conversion between a current block in a video region of a video and a coded representation of the video, and performing the conversion based on the position rule. The position rule specifies that the LIC tool is enabled for blocks on boundaries of the video region and disabled for blocks inside the video region and the LIC tool includes using a linear model of illumination changes in the current block during the conversion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/230,048, filed on Apr. 14, 2021, which is a continuation ofInternational Application No. PCT/IB2019/059042, filed on Oct. 23, 2019,which claims the priority to and benefits of International PatentApplication No. PCT/CN2018/111436, filed on Oct. 23, 2018, InternationalPatent Application No. PCT/CN2019/071759, filed on Jan. 15, 2019, andInternational Patent Application No. PCT/CN2019/072154, filed on Jan.17, 2019. All the aforementioned patent applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the field of video processing.

BACKGROUND

Currently, efforts are underway to improve the performance of currentvideo codec technologies to provide better compression ratios or providevideo coding and decoding schemes that allow for lower complexity orparallelized implementations. Industry experts have recently proposedseveral new video coding tools and tests are currently underway fordetermining their effectivity.

SUMMARY

The present disclosure provides techniques for incorporating localillumination compensation in embodiments of video encoders or decoders.

In one example aspect, a video processing method is disclosed. The videoprocessing method comprises: determining, based on a position rule,whether a local illumination compensation (LIC) tool is enabled for aconversion between a current block in a video region of a video and acoded representation of the video, and performing the conversion basedon the position rule. The position rule specifies that the LIC tool isenabled for blocks on boundaries of the video region and disabled forblocks inside the video region and the LIC tool includes using a linearmodel of illumination changes in the current block during theconversion.

In another example aspect, a video processing method is disclosed. Thevideo processing method comprises: determining, a procedure for derivinglocal illumination compensation parameters used for a conversion betweena current video block of a video region or a video and a codedrepresentation of the video based on a position rule of the currentvideo block in the video region; and performing the conversion based onthe determining.

In another example aspect, a video processing method is provided. Thevideo processing method comprises: determining, for a conversion betweena current block in a video region of a video and a coded representationof the video, local illumination compensation (LIC) parameters for a LICoperation using at least some samples of neighboring blocks of thecurrent block; and performing the conversion using the determined LICparameters, wherein the LIC operation includes using a linear model ofillumination changes in the current block during the conversion.

In another example aspect, a video processing method is provided. Thevideo processing method comprises: performing a conversion between acurrent block in a video region of a video and a coded representation ofthe video, wherein the video is represented as video frames comprisingvideo blocks, and a local illumination compensation (LIC) tool isenabled for video blocks that use a geometric prediction structureincluding a triangular prediction mode, wherein the LIC tool includesusing a linear model of illumination changes in the current block duringthe conversion.

In another example aspect, a video processing method is provided. Thevideo processing method comprises: performing a conversion between acurrent block in a video region of a video and a coded representation ofthe video, wherein the video is represented as video frames comprisingvideo blocks, and a local illumination compensation (LIC) operation isperformed for less than all pixels of the current block, wherein the LICoperation includes using a linear model of illumination changes in thecurrent block during the conversion.

In another example aspect, a video processing method is provided. Thevideo processing method comprises: determining that a local illuminationcompensation (LIC) operation is to be performed; dividing a currentblock into video processing data units (VPDUs) based on thedetermination that the LIC operation is to be performed; and performingthe LIC operation in sequence or in parallel for the VPDUs, wherein theLIC operation includes using a linear model of illumination changes inthe current block during the conversion.

In one example aspect, a video processing method is disclosed. The videoprocessing method comprises: determining to use a rule that specifiesthat at most a single coding tool from a set of coding tools is used fora conversion between a current block of a video comprising multiplepictures and a coded representation of the video, and performing theconversion based on the rule. The set of coding tools include codingtools that modify a reconstructed block of the current block generatedfrom motion information from the coded representation or an interprediction signal generated for the current block during the conversion.

In another example aspect, a video processing method is disclosed. Thevideo processing method comprises: determining, for a conversion betweena current block of a video and a coded representation of the video, thatboth local illumination compensation (LIC) and combined inter-intraprediction (CIIP) coding tools are enabled for the conversion of thecurrent block; and performing the conversion based on the determining.

In yet another representative aspect, the various techniques describedherein may be embodied as a computer program product stored on anon-transitory computer readable media. The computer program productincludes program code for carrying out the methods described herein.

In yet another representative aspect, a video decoder apparatus mayimplement a method as described herein.

The details of one or more implementations are set forth in theaccompanying attachments, the drawings, and the description below. Otherfeatures will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a derivation process for merge candidateslist construction.

FIG. 2 shows example positions of spatial merge candidates.

FIG. 3 shows examples of candidate pairs considered for redundancy checkof spatial merge candidates.

FIG. 4 shows example positions for the second prediction unit (PU) ofN×2N and 2N×N partitions.

FIG. 5 is an Illustration of motion vector scaling for temporal mergecandidate.

FIG. 6 shows examples of candidate positions for temporal mergecandidate, C0 and C1.

FIG. 7 shows an example of combined bi-predictive merge candidate

FIG. 8 shows an example of a derivation process for motion vectorprediction candidates.

FIG. 9 is an example illustration of motion vector scaling for spatialmotion vector candidate.

FIG. 10 illustrates an example of advanced temporal motion vectorpredictor (ATMVP) for a Coding Unit (CU).

FIG. 11 shows an Example of one CU with four sub-blocks (A-D) and itsneighboring blocks (a-d).

FIG. 12 shows an example of a planar motion vector prediction process.

FIG. 13 is a flowchart of an example of encoding with different motionvector (MV) precision.

FIG. 14 is an example Illustration of sub-blocks where Overlapped BlockMotion Compensation (OBMC) applies.

FIG. 15 shows an example of neighboring samples used for derivingillumination compensation (IC) parameters.

FIG. 16 is an illustration of splitting a coding unit (CU) into twotriangular prediction units.

FIG. 17 shows an example of positions of neighboring blocks.

FIG. 18 shows an example in which a CU applies the 1^(st) weightingfactor group.

FIG. 19 shows an example of motion vector storage implementation.

FIG. 20 shows an example of a simplified affine motion model.

FIG. 21 shows an example of affine motion vector field (MVF) persub-block.

FIG. 22 shows examples of (a) 4-parameter affine model (b) and6-parameter affine model.

FIG. 23 shows an example of a Motion Vector Predictor (MV) for AF_INTERmode.

FIG. 24A-24B shows examples of candidates for AF_MERGE mode.

FIG. 25 shows candidate positions for affine merge mode.

FIG. 26 shows example process for bilateral matching.

FIG. 27 shows example process of template matching.

FIG. 28 illustrates an implementation of unilateral motion estimation(ME) in frame rate upconversion (FRUC).

FIG. 29 illustrates an embodiment of an Ultimate Motion VectorExpression (UMVE) search process.

FIG. 30 shows examples of UMVE search points.

FIG. 31 shows an example of distance index and distance offset mapping.

FIG. 32 shows an example of an optical flow trajectory.

FIG. 33A-33B show examples of Bi-directional Optical flow (BIO) withoutblock extension: a) access positions outside of the block; b) paddingused in order to avoid extra memory access and calculation.

FIG. 34 illustrates an example of using Decoder-side motion vectorrefinement (DMVR) based on bilateral template matching.

FIG. 35 shows an example of neighboring samples used in a bilateralfilter.

FIG. 36 shows an example of windows covering two samples used in weightcalculation.

FIG. 37 shows an example of a decoding flow with the proposed historybased motion vector prediction (HMVP) method.

FIG. 38 shows an example of updating the table in the proposed HMVPmethod.

FIG. 39 is a block diagram of a hardware platform for implementing thevideo coding or decoding techniques described in the present disclosure.

FIG. 40A shows an example of a hardware platform for implementingmethods and techniques described in the present disclosure.

FIG. 40B shows another example of a hardware platform for implementingmethods and techniques described in the present disclosure.

FIGS. 41A-41H are flowcharts of example methods of video processing.

DETAILED DESCRIPTION

The present disclosure provides several techniques that can be embodiedinto digital video encoders and decoders. Section headings are used inthe present disclosure for clarity of understanding and do not limitscope of the techniques and embodiments disclosed in each section onlyto that section.

1. Summary

The present disclosure is related to video coding technologies.Specifically, it is related to local illumination compensation (LIC) invideo coding. It may be applied to the existing video coding standardlike High Efficiency Video Coding (HEVC), or the standard VersatileVideo Coding (VVC) to be finalized. It may be also applicable to futurevideo coding standards or video codec.

2. Examples of Video Coding/Decoding Technologies

Video coding standards have evolved primarily through the development ofthe well-known International Telecommunication Union—TelecommunicationStandardization Sector (ITU-T) and International Organization forStandardization (ISO)/International Electrotechnical Commission (IEC)standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MovingPicture Experts Group (MPEG)-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Toexplore the future video coding technologies beyond HEVC, Joint VideoExploration Team (JVET) was founded by Video Coding Experts Group (VCEG)and MPEG jointly in 2015. Since then, many new methods have been adoptedby JVET and put into the reference software named Joint ExplorationModel (JEM). In April 2018, the Joint Video Expert Team (JVET) betweenVCEG (Q6/16) and ISO/IEC Joint Technical Committee (JTC1) SC29/WG11(MPEG) was created to work on the VVC standard targeting at 50% bitratereduction compared to HEVC.

The latest version of VVC draft, i.e., Versatile Video Coding (Draft 2)could be found at:

http://phenix.it-sudparis.eu/jvet/doc_end_user/documents/11_Ljubljana/wg11/JVET-K1001-v7.zip

The latest reference software of VVC, named VTM, could be found at:

https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/tags/VTM-2.1

2.1. Inter Prediction in HEVC/H.265

Each inter-predicted PU has motion parameters for one or two referencepicture lists. Motion parameters include a motion vector and a referencepicture index. Usage of one of the two reference picture lists may alsobe signalled using inter_pred_idc. Motion vectors may be explicitlycoded as deltas relative to predictors.

When a CU is coded with skip mode, one PU is associated with the CU, andthere are no significant residual coefficients, no coded motion vectordelta or reference picture index. A merge mode is specified whereby themotion parameters for the current PU are obtained from neighboring PUs,including spatial and temporal candidates. The merge mode can be appliedto any inter-predicted PU, not only for skip mode. The alternative tomerge mode is the explicit transmission of motion parameters, wheremotion vector (to be more precise, motion vector difference compared toa motion vector predictor), corresponding reference picture index foreach reference picture list and reference picture list usage aresignalled explicitly per each PU. Such a mode is named advanced motionvector prediction (AMVP) in this disclosure.

When signalling indicates that one of the two reference picture lists isto be used, the PU is produced from one block of samples. This isreferred to as ‘uni-prediction’. Uni-prediction is available both forP-slices and B-slices.

When signalling indicates that both of the reference picture lists areto be used, the PU is produced from two blocks of samples. This isreferred to as ‘bi-prediction’. Bi-prediction is available for B-slicesonly.

The following text provides the details on the inter prediction modesspecified in HEVC. The description will start with the merge mode.

2.1.1. Merge Mode 2.1.1.1. Derivation of Candidates for Merge Mode

When a PU is predicted using merge mode, an index pointing to an entryin the merge candidates list is parsed from the bitstream and used toretrieve the motion information. The construction of this list isspecified in the HEVC standard and can be summarized according to thefollowing sequence of steps:

-   -   Step 1: Initial candidates derivation        -   Step 1.1: Spatial candidates derivation        -   Step 1.2: Redundancy check for spatial candidates        -   Step 1.3: Temporal candidates derivation    -   Step 2: Additional candidates insertion        -   Step 2.1: Creation of bi-predictive candidates        -   Step 2.2: Insertion of zero motion candidates

These steps are also schematically depicted in FIG. 1 . For spatialmerge candidate derivation, a maximum of four merge candidates areselected among candidates that are located in five different positions.For temporal merge candidate derivation, a maximum of one mergecandidate is selected among two candidates. Since constant number ofcandidates for each PU is assumed at decoder, additional candidates aregenerated when the number of candidates obtained from step 1 does notreach the maximum number of merge candidate (MaxNumMergeCand) which issignalled in slice header. Since the number of candidates is constant,index of best merge candidate is encoded using truncated unarybinarization (TU). If the size of CU is equal to 8, all the PUs of thecurrent CU share a single merge candidate list, which is identical tothe merge candidate list of the 2N×2N prediction unit.

In the following, the operations associated with the aforementionedsteps are detailed.

2.1.1.2. Spatial Candidates Derivation

In the derivation of spatial merge candidates, a maximum of four mergecandidates are selected among candidates located in the positionsdepicted in FIG. 2 . The order of derivation is A₁, B₁, B₀, A₀ and B₂.Position B₂ is considered only when any PU of position A₁, B₁, B₀, A₀ isnot available (e.g., because it belongs to another slice or tile) or isintra coded. After candidate at position A₁ is added, the addition ofthe remaining candidates is subject to a redundancy check which ensuresthat candidates with same motion information are excluded from the listso that coding efficiency is improved. FIG. 3 shows examples ofcandidate pairs considered for redundancy check of spatial mergecandidates. To reduce computational complexity, not all possiblecandidate pairs are considered in the mentioned redundancy check.Instead only the pairs linked with an arrow in FIG. 3 are considered anda candidate is only added to the list if the corresponding candidateused for redundancy check has not the same motion information. Anothersource of duplicate motion information is the “second PU” associatedwith partitions different from 2N×2N. As an example, FIG. 4 depicts thesecond PU for the case of N×2N and 2N×N, respectively. When the currentPU is partitioned as N×2N, candidate at position A₁ is not consideredfor list construction. In fact, by adding this candidate will lead totwo prediction units having the same motion information, which isredundant to just have one PU in a coding unit. Similarly, position Biis not considered when the current PU is partitioned as 2N×N.

2.1.1.3. Temporal Candidates Derivation

In this step, only one candidate is added to the list. Particularly, inthe derivation of this temporal merge candidate, a scaled motion vectoris derived based on co-located PU belonging to the picture which has thesmallest picture order count (POC) difference with current picturewithin the given reference picture list. The reference picture list tobe used for derivation of the co-located PU is explicitly signalled inthe slice header. FIG. 5 is an Illustration of motion vector scaling fortemporal merge candidate. The scaled motion vector for temporal mergecandidate is obtained as illustrated by the dotted line in FIG. 5 ,which is scaled from the motion vector of the co-located PU using thePOC distances, tb and td, where tb is defined to be the POC differencebetween the reference picture of the current picture and the currentpicture and td is defined to be the POC difference between the referencepicture of the co-located picture and the co-located picture. Thereference picture index of temporal merge candidate is set equal tozero. A practical realization of the scaling process is described in theHEVC specification. For a B-slice, two motion vectors, one is forreference picture list 0 and the other is for reference picture list 1,are obtained and combined to make the bi-predictive merge candidate.

In the co-located PU (Y) belonging to the reference frame, the positionfor the temporal candidate is selected between candidates C₀ and C₁, asdepicted in FIG. 6 . If PU at position C₀ is not available, is intracoded, or is outside of the current coding tree unit (CTU) row, positionC₁ is used. Otherwise, position C₀ is used in the derivation of thetemporal merge candidate.

2.1.1.4. Additional Candidates Insertion

Besides spatial and temporal merge candidates, there are two additionaltypes of merge candidates: combined bi-predictive merge candidate andzero merge candidate. Combined bi-predictive merge candidates aregenerated by utilizing spatial and temporal merge candidates. Combinedbi-predictive merge candidate is used for B-Slice only. The combinedbi-predictive candidates are generated by combining the first referencepicture list motion parameters of an initial candidate with the secondreference picture list motion parameters of another. If these two tuplesprovide different motion hypotheses, they will form a new bi-predictivecandidate. As an example, FIG. 7 depicts the case when two candidates inthe original list (on the left), which have mvL0 and refIdxL0 or mvL1and refIdxL1, are used to create a combined bi-predictive mergecandidate added to the final list (on the right). There are numerousrules regarding the combinations which are considered to generate theseadditional merge candidates.

Zero motion candidates are inserted to fill the remaining entries in themerge candidates list and therefore hit the MaxNumMergeCand capacity.These candidates have zero spatial displacement and a reference pictureindex which starts from zero and increases every time a new zero motioncandidate is added to the list. The number of reference frames used bythese candidates is one and two for uni and bi-directional prediction,respectively. Finally, no redundancy check is performed on thesecandidates.

2.1.1.5. Motion Estimation Regions for Parallel Processing

To speed up the encoding process, motion estimation can be performed inparallel whereby the motion vectors for all prediction units inside agiven region are derived simultaneously. The derivation of mergecandidates from spatial neighbourhood may interfere with parallelprocessing as one prediction unit cannot derive the motion parametersfrom an adjacent PU until its associated motion estimation is completed.To mitigate the trade-off between coding efficiency and processinglatency, HEVC defines the motion estimation region (MER) whose size issignalled in the picture parameter set using the “log2_parallel_merge_level_minus2” syntax element. When a MER is defined,merge candidates falling in the same region are marked as unavailableand therefore not considered in the list construction.

2.1.2. AMVP

AMVP exploits spatio-temporal correlation of motion vector withneighboring PUs, which is used for explicit transmission of motionparameters. For each reference picture list, a motion vector candidatelist is constructed by firstly checking availability of left, abovetemporally neighboring PU positions, removing redundant candidates andadding zero vector to make the candidate list to be constant length.Then, the encoder can select the best predictor from the candidate listand transmit the corresponding index indicating the chosen candidate.Similarly with merge index signalling, the index of the best motionvector candidate is encoded using truncated unary. The maximum value tobe encoded in this case is 2 (see FIG. 8 ). In the following sections,details about derivation process of motion vector prediction candidateare provided.

2.1.2.1. Derivation of AMVP Candidates

In motion vector prediction, two types of motion vector candidates areconsidered: spatial motion vector candidate and temporal motion vectorcandidate. For spatial motion vector candidate derivation, two motionvector candidates are eventually derived based on motion vectors of eachPU located in five different positions as depicted in FIG. 2 .

For temporal motion vector candidate derivation, one motion vectorcandidate is selected from two candidates, which are derived based ontwo different co-located positions. After the first list ofspatio-temporal candidates is made, duplicated motion vector candidatesin the list are removed. If the number of potential candidates is largerthan two, motion vector candidates whose reference picture index withinthe associated reference picture list is larger than 1 are removed fromthe list. If the number of spatio-temporal motion vector candidates issmaller than two, additional zero motion vector candidates is added tothe list.

2.1.2.2. Spatial Motion Vector Candidates

In the derivation of spatial motion vector candidates, a maximum of twocandidates are considered among five potential candidates, which arederived from PUs located in positions as depicted in FIG. 2 , thosepositions being the same as those of motion merge. The order ofderivation for the left side of the current PU is defined as A₀, A₁, andscaled A₀, scaled A₁. The order of derivation for the above side of thecurrent PU is defined as B₀, B₁, B₂, scaled B₀, scaled B₁, scaled B₂.For each side there are therefore four cases that can be used as motionvector candidate, with two cases not required to use spatial scaling,and two cases where spatial scaling is used. The four different casesare summarized as follows.

-   -   No spatial scaling        -   (1) Same reference picture list, and same reference picture            index (same POC)        -   (2) Different reference picture list, but same reference            picture (same POC) Spatial scaling        -   (3) Same reference picture list, but different reference            picture (different POC)        -   (4) Different reference picture list, and different            reference picture (different POC)

The no-spatial-scaling cases are checked first followed by the spatialscaling. Spatial scaling is considered when the POC is different betweenthe reference picture of the neighboring PU and that of the current PUregardless of reference picture list. If all PUs of left candidates arenot available or are intra coded, scaling for the above motion vector isallowed to help parallel derivation of left and above MV candidates.Otherwise, spatial scaling is not allowed for the above motion vector.

In a spatial scaling process, the motion vector of the neighboring PU isscaled in a similar manner as for temporal scaling, as depicted as FIG.9 . The main difference is that the reference picture list and index ofcurrent PU is given as input; the actual scaling process is the same asthat of temporal scaling.

2.1.2.3. Temporal Motion Vector Candidates

Apart for the reference picture index derivation, all processes for thederivation of temporal merge candidates are the same as for thederivation of spatial motion vector candidates (see FIG. 6 ). Thereference picture index is signalled to the decoder.

2.2. New Inter Prediction Methods in JEM 2.2.1. Sub-CU Based MotionVector Prediction

In the JEM with quad tree binary tree (QTBT), each CU can have at mostone set of motion parameters for each prediction direction. Two sub-CUlevel motion vector prediction methods are considered in the encoder bysplitting a large CU into sub-CUs and deriving motion information forall the sub-CUs of the large CU. Alternative temporal motion vectorprediction (ATMVP) method allows each CU to fetch multiple sets ofmotion information from multiple blocks smaller than the current CU inthe collocated reference picture. In spatial-temporal motion vectorprediction (STMVP) method motion vectors of the sub-CUs are derivedrecursively by using the temporal motion vector predictor and spatialneighboring motion vector.

To preserve more accurate motion field for sub-CU motion prediction, themotion compression for the reference frames is currently disabled.

2.2.1.1. Alternative Temporal Motion Vector Prediction

In the alternative temporal motion vector prediction (ATMVP) method, themotion vectors temporal motion vector prediction (TMVP) is modified byfetching multiple sets of motion information (including motion vectorsand reference indices) from blocks smaller than the current CU. As shownin FIG. 10 , the sub-CUs are square N×N blocks (N is set to 4 bydefault).

ATMVP predicts the motion vectors of the sub-CUs within a CU in twosteps. The first step is to identify the corresponding block in areference picture with a so-called temporal vector. The referencepicture is called the motion source picture. The second step is to splitthe current CU into sub-CUs and obtain the motion vectors as well as thereference indices of each sub-CU from the block corresponding to eachsub-CU, as shown in FIG. 10 .

In the first step, a reference picture and the corresponding block isdetermined by the motion information of the spatial neighboring blocksof the current CU. To avoid the repetitive scanning process ofneighboring blocks, the first merge candidate in the merge candidatelist of the current CU is used. The first available motion vector aswell as its associated reference index are set to be the temporal vectorand the index to the motion source picture. This way, in ATMVP, thecorresponding block may be more accurately identified, compared withTMVP, wherein the corresponding block (sometimes called collocatedblock) is always in a bottom-right or center position relative to thecurrent CU.

In the second step, a corresponding block of the sub-CU is identified bythe temporal vector in the motion source picture, by adding to thecoordinate of the current CU the temporal vector. For each sub-CU, themotion information of its corresponding block (the smallest motion gridthat covers the center sample) is used to derive the motion informationfor the sub-CU. After the motion information of a corresponding N×Nblock is identified, it is converted to the motion vectors and referenceindices of the current sub-CU, in the same way as TMVP of HEVC, whereinmotion scaling and other procedures apply. For example, the decoderchecks whether the low-delay condition (i.e., the POCs of all referencepictures of the current picture are smaller than the POC of the currentpicture) is fulfilled and possibly uses motion vector MV_(x) (the motionvector corresponding to reference picture list X) to predict motionvector MV_(y) (with X being equal to 0 or 1 and Y being equal to 1−X)for each sub-CU.

2.2.1.2. Spatial-Temporal Motion Vector Prediction

In this method, the motion vectors of the sub-CUs are derivedrecursively, following raster scan order. FIG. 11 illustrates thisconcept. Let us consider an 8×8 CU which contains four 4×4 sub-CUs A, B,C, and D. The neighboring 4×4 blocks in the current frame are labelledas a, b, c, and d.

The motion derivation for sub-CU A starts by identifying its two spatialneighbours. The first neighbour is the N×N block above sub-CU A (blockc). If this block c is not available or is intra coded the other N×Nblocks above sub-CU A are checked (from left to right, starting at blockc). The second neighbour is a block to the left of the sub-CU A (blockb). If block b is not available or is intra coded other blocks to theleft of sub-CU A are checked (from top to bottom, staring at block b).The motion information obtained from the neighboring blocks for eachlist is scaled to the first reference frame for a given list. Next,temporal motion vector predictor (TMVP) of sub-block A is derived byfollowing the same procedure of TMVP derivation as specified in HEVC.The motion information of the collocated block at location D is fetchedand scaled accordingly. Finally, after retrieving and scaling the motioninformation, all available motion vectors (up to 3) are averagedseparately for each reference list. The averaged motion vector isassigned as the motion vector of the current sub-CU.

2.2.1.3. Sub-CU Motion Prediction Mode Signalling

The sub-CU modes are enabled as additional merge candidates and there isno additional syntax element required to signal the modes. Twoadditional merge candidates are added to merge candidates list of eachCU to represent the ATMVP mode and STMVP mode. Up to seven mergecandidates are used, if the sequence parameter set indicates that ATMVPand STMVP are enabled. The encoding logic of the additional mergecandidates is the same as for the merge candidates in the HM, whichmeans, for each CU in P or B slice, two more rate distortion (RD) checksis needed for the two additional merge candidates.

In the JEM, all bins of merge index are context coded bycontext-adaptive binary arithmetic coding (CABAC). While in HEVC, onlythe first bin is context coded and the remaining bins are contextby-pass coded.

2.2.2. Pairwise Average Candidates

Pairwise average candidates are generated by averaging predefined pairsof candidates in the current merge candidate list, and the predefinedpairs are defined as {(0, 1), (0, 2), (1, 2), (0, 3), (1, 3), (2, 3)},where the numbers denote the merge indices to the merge candidate list.The averaged motion vectors are calculated separately for each referencelist. If both motion vectors are available in one list, these two motionvectors are averaged even when they point to different referencepictures; if only one motion vector is available, use the one directly;if no motion vector is available, keep this list invalid. The pairwiseaverage candidates replace the combined candidates in HEVC standard.

The complexity analysis of pairwise average candidates is summarized inthe Table 1. For the worst case of additional calculations for averaging(the last column in Table 1), 4 additions and 4 shifts are needed foreach pair (MVx and MVy in L0 and L1), and 4 reference index comparisonsare needed for each pair (refIdx0 is valid and refIdx1 is valid in L0and L1). There are 6 pairs, leading to 24 additions, 24 shifts, and 24reference index comparisons in total. The combined candidates in HEVCstandard use 2 reference index comparisons for each pair (refIdx0 isvalid in L0 and refIdx1 is valid in L1), and there are 12 pairs, leadingto 24 reference index comparisons in total.

TABLE 1 Operation analysis for the pairwise average candidates Max MaxMax Max Max Merge number of number of number of number of Additionalnumber of list potential candidate MV temporal local memory sizecandidates comparisons scalings candidates buffer access Others 6, 8, 106 0 0 0 0 0 Replace HEVC combined candidates, need additionalcalculations for averaging

2.2.3. Planar Motion Vector Prediction

In JVET-K0135, planar motion vector prediction is proposed.

To generate a smooth fine granularity motion field, FIG. 12 gives abrief description of the planar motion vector prediction process.

Planar motion vector prediction is achieved by averaging a horizontaland vertical linear interpolation on 4×4 block basis as follows:

P(x,y)=(H×P _(h)(x,y)+W×P _(v)(x,y)+H×W)/(2×H×W)  Eq.(1)

W and H denote the width and the height of the block. (x,y) is thecoordinates of current sub-block relative to the above left cornersub-block. All the distances are denoted by the pixel distances dividedby 4. P(x, y) is the motion vector of current sub-block.

The horizontal prediction P_(h)(x, y) and the vertical predictionP_(v)(x, y) for location (x,y) are calculated as follows:

P _(h)(x,y)=(W−1−x)×L(−1,y)+(x+1)×R(W,y)  Eq.(2)

P _(v)(x,y)=(H−1−y)×A(x,−1)+(y+1)×B(x,H)  Eq.(3)

where L(−1, y) and R(W, y) are the motion vectors of the 4×4 blocks tothe left and right of the current block. A(x,−1) and B(x, H) are themotion vectors of the 4×4 blocks to the above and bottom of the currentblock.

The reference motion information of the left column and above rowneighbour blocks are derived from the spatial neighbour blocks ofcurrent block.

The reference motion information of the right column and bottom rowneighbour blocks are derived as follows.

-   -   1) Derive the motion information of the bottom right temporal        neighbour 4×4 block    -   2) Compute the motion vectors of the right column neighbour 4×4        blocks, using the derived motion information of the bottom right        neighbour 4×4 block along with the motion information of the        above right neighbour 4×4 block, as described in Eq. (4).    -   3) Compute the motion vectors of the bottom row neighbour 4×4        blocks, using the derived motion information of the bottom right        neighbour 4×4 block along with the motion information of the        bottom left neighbour 4×4 block, as described in Eq. (5).

R(W,y)=((H−y−1)×AR+(y+1)×BR)/H  Eq. (4)

B(x,H)=((W−x−1)×BL+(x+1)×BR)/W  Eq. (5)

-   -    where AR is the motion vector of the above right spatial        neighbour 4×4 block, BR is the motion vector of the bottom right        temporal neighbour 4×4 block, and BL is the motion vector of the        bottom left spatial neighbour 4×4 block.

The motion information obtained from the neighboring blocks for eachlist is scaled to the first reference picture for a given list.

2.2.4. Adaptive Motion Vector Difference Resolution

In HEVC, motion vector differences (MVDs) (between the motion vector andpredicted motion vector of a PU) are signalled in units of quarter lumasamples when use_integer_mv_flag is equal to 0 in the slice header. Inthe JEM, a locally adaptive motion vector resolution (LAMVR) isintroduced. In the JEM, MVD can be coded in units of quarter lumasamples, integer luma samples or four luma samples. The MVD resolutionis controlled at the coding unit (CU) level, and MVD resolution flagsare conditionally signalled for each CU that has at least one non-zeroMVD components.

For a CU that has at least one non-zero MVD components, a first flag issignalled to indicate whether quarter luma sample MV precision is usedin the CU. When the first flag (equal to 1) indicates that quarter lumasample MV precision is not used, another flag is signalled to indicatewhether integer luma sample MV precision or four luma sample MVprecision is used.

When the first MVD resolution flag of a CU is zero, or not coded for aCU (meaning all MVDs in the CU are zero), the quarter luma sample MVresolution is used for the CU. When a CU uses integer-luma sample MVprecision or four-luma-sample MV precision, the MVPs in the AMVPcandidate list for the CU are rounded to the corresponding precision.

In the encoder, CU-level RD checks are used to determine which MVDresolution is to be used for a CU. That is, the CU-level RD check isperformed three times for each MVD resolution. To accelerate encoderspeed, the following encoding schemes are applied in the JEM.

-   -   During RD check of a CU with normal quarter luma sample MVD        resolution, the motion information of the current CU (integer        luma sample accuracy) is stored. The stored motion information        (after rounding) is used as the starting point for further small        range motion vector refinement during the RD check for the same        CU with integer luma sample and 4 luma sample MVD resolution so        that the time-consuming motion estimation process is not        duplicated three times.    -   RD check of a CU with 4 luma sample MVD resolution is        conditionally invoked. For a CU, when RD cost integer luma        sample MVD resolution is much larger than that of quarter luma        sample MVD resolution, the RD check of 4 luma sample MVD        resolution for the CU is skipped.

The encoding process is shown in FIG. 13 . First, ¼ pel MV is tested andthe RD cost is calculated and denoted as RDCost0, then integer MV istested and the RD cost is denoted as RDCost1. If RDCost1<th*RDCost0(wherein th is a positive value), then 4-pel MV is tested; otherwise,4-pel MV is skipped. Basically, motion information and RD cost etc. arealready known for ¼ pel MV when checking integer or 4-pel MV, which canbe reused to speed up the encoding process of integer or 4-pel MV.

2.2.5. Higher Motion Vector Storage Accuracy

In HEVC, motion vector accuracy is one-quarter pel (one-quarter lumasample and one-eighth chroma sample for 4:2:0 video). In the JEM, theaccuracy for the internal motion vector storage and the merge candidateincreases to 1/16 pel. The higher motion vector accuracy ( 1/16 pel) isused in motion compensation inter prediction for the CU coded withskip/merge mode. For the CU coded with normal AMVP mode, either theinteger-pel or quarter-pel motion is used, as described in section2.2.2.

SHVC upsampling interpolation filters, which have same filter length andnormalization factor as HEVC motion compensation interpolation filters,are used as motion compensation interpolation filters for the additionalfractional pel positions. The chroma component motion vector accuracy is1/32 sample in the JEM, the additional interpolation filters of 1/32 pelfractional positions are derived by using the average of the filters ofthe two neighboring 1/16 pel fractional positions.

2.2.6. Overlapped Block Motion Compensation

Overlapped Block Motion Compensation (OBMC) has previously been used inH.263. In the JEM, unlike in H.263, OBMC can be switched on and offusing syntax at the CU level. When OBMC is used in the JEM, the OBMC isperformed for all motion compensation (MC) block boundaries except theright and bottom boundaries of a CU. Moreover, it is applied for boththe luma and chroma components. In the JEM, a MC block is correspondingto a coding block. When a CU is coded with sub-CU mode (includes sub-CUmerge, affine and FRUC mode), each sub-block of the CU is a MC block. Toprocess CU boundaries in a uniform fashion, OBMC is performed atsub-block level for all MC block boundaries, where sub-block size is setequal to 4×4, as illustrated in FIG. 14 .

When OBMC applies to the current sub-block, besides current motionvectors, motion vectors of four connected neighboring sub-blocks, ifavailable and are not identical to the current motion vector, are alsoused to derive prediction block for the current sub-block. Thesemultiple prediction blocks based on multiple motion vectors are combinedto generate the final prediction signal of the current sub-block.

Prediction block based on motion vectors of a neighboring sub-block isdenoted as P_(N), with N indicating an index for the neighboring above,below, left and right sub-blocks and prediction block based on motionvectors of the current sub-block is denoted as P_(C). When P_(N) isbased on the motion information of a neighboring sub-block that containsthe same motion information to the current sub-block, the OBMC is notperformed from P_(N). Otherwise, every sample of P_(N) is added to thesame sample in P_(C), i.e., four rows/columns of P_(N) are added toP_(C). The weighting factors {¼, ⅛, 1/16, 1/32} are used for P_(N) andthe weighting factors {¾, ⅞, 15/16, 31/32} are used for P_(C). Theexception are small MC blocks, (i.e., when height or width of the codingblock is equal to 4 or a CU is coded with sub-CU mode), for which onlytwo rows/columns of P_(N) are added to P_(C). In this case weightingfactors {¼, ⅛} are used for P_(N) and weighting factors {¾, ⅞} are usedfor P_(C). For P_(N) generated based on motion vectors of vertically(horizontally) neighboring sub-block, samples in the same row (column)of P_(N) are added to P_(C) with a same weighting factor.

In the JEM, for a CU with size less than or equal to 256 luma samples, aCU level flag is signalled to indicate whether OBMC is applied or notfor the current CU. For the CUs with size larger than 256 luma samplesor not coded with AMVP mode, OBMC is applied by default. At the encoder,when OBMC is applied for a CU, its impact is taken into account duringthe motion estimation stage. The prediction signal formed by OBMC usingmotion information of the top neighboring block and the left neighboringblock is used to compensate the top and left boundaries of the originalsignal of the current CU, and then the normal motion estimation processis applied.

2.2.7. Local Illumination Compensation

Local Illumination Compensation (LIC) is based on a linear model forillumination changes, using a scaling factor a and an offset b. And itis enabled or disabled adaptively for each inter-mode coded coding unit(CU).

When LIC applies for a CU, a least square error method is employed toderive the parameters a and b by using the neighboring samples of thecurrent CU and their corresponding reference samples. More specifically,as illustrated in FIG. 15 , the subsampled (2:1 subsampling) neighboringsamples of the CU and the corresponding samples (identified by motioninformation of the current CU or sub-CU) in the reference picture areused. The IC parameters are derived and applied for each predictiondirection separately.

When a CU is coded with merge mode, the LIC flag is copied fromneighboring blocks, in a way similar to motion information copy in mergemode; otherwise, an LIC flag is signalled for the CU to indicate whetherLIC applies or not.

When LIC is enabled for a picture, additional CU level RD check isneeded to determine whether LIC is applied or not for a CU. When LIC isenabled for a CU, mean-removed sum of absolute difference (MR-SAD) andmean-removed sum of absolute Hadamard-transformed difference (MR-SATD)are used, instead of SAD and SATD, for integer pel motion search andfractional pel motion search, respectively.

To reduce the encoding complexity, the following encoding scheme isapplied in the JEM. LIC is disabled for the entire picture when there isno obvious illumination change between a current picture and itsreference pictures. To identify this situation, histograms of a currentpicture and every reference picture of the current picture arecalculated at the encoder. If the histogram difference between thecurrent picture and every reference picture of the current picture issmaller than a given threshold, LIC is disabled for the current picture;otherwise, LIC is enabled for the current picture.

2.2.8. Hybrid Intra and Inter Prediction

In JVET-L0100, multi-hypothesis prediction is proposed, wherein hybridintra and inter prediction is one way to generate multiple hypotheses.

When the multi-hypothesis prediction is applied to improve intra mode,multi-hypothesis prediction combines one intra prediction and one mergeindexed prediction. In a merge CU, one flag is signaled for merge modeto select an intra mode from an intra candidate list when the flag istrue. For luma component, the intra candidate list is derived from 4intra prediction modes including direct current (DC), planar,horizontal, and vertical modes, and the size of the intra candidate listcan be 3 or 4 depending on the block shape. When the CU width is largerthan the double of CU height, horizontal mode is exclusive of the intramode list and when the CU height is larger than the double of CU width,vertical mode is removed from the intra mode list. One intra predictionmode selected by the intra mode index and one merge indexed predictionselected by the merge index are combined using weighted average. Forchroma component, derived mode (DM) is always applied without extrasignaling. The weights for combining predictions are described asfollow. When DC or planar mode is selected, or the blue differencechroma (CB) width or height is smaller than 4, equal weights areapplied. For those CBs with CB width and height larger than or equal to4, when horizontal/vertical mode is selected, one CB is firstvertically/horizontally split into four equal-area regions. Each weightset, denoted as (w_intra_(i), w_inter_(i)), where i is from 1 to 4 and(w_intra₁, w_inter₁)=(6, 2), (w_intra₂, w_inter₂)=(5, 3), (w_intra₃,w_inter₃)=(3, 5), and (w_intra₄, w_inter₄)=(2, 6), will be applied to acorresponding region. (w_intra₁, w_inter₁) is for the region closest tothe reference samples and (w_intra₄, w_inter₄) is for the regionfarthest away from the reference samples. Then, the combined predictioncan be calculated by summing up the two weighted predictions andright-shifting 3 bits. Moreover, the intra prediction mode for the intrahypothesis of predictors can be saved for reference of the followingneighboring CUs.

Such method is also known as combined intra-inter Prediction (CIIP).

2.2.9. Triangular Prediction Unit Mode

The concept of the triangular prediction unit mode is to introduce a newtriangular partition for motion compensated prediction. As shown in FIG.16 , it splits a CU into two triangular prediction units (PUs), ineither diagonal or inverse diagonal direction. Each triangularprediction unit in the CU is inter-predicted using its ownuni-prediction motion vector and reference frame index which are derivedfrom a uni-prediction candidate list. An adaptive weighting process isperformed to the diagonal edge after predicting the triangularprediction units. Then, the transform and quantization process areapplied to the whole CU. It is noted that this mode is only applied toskip and merge modes.

Uni-Prediction Candidate List

The uni-prediction candidate list consists of five uni-prediction motionvector candidates. It is derived from seven neighboring blocks includingfive spatial neighboring blocks (1 to 5) and two temporal co-locatedblocks (6 to 7), as shown in FIG. 17 . The motion vectors of the sevenneighboring blocks are collected and put into the uni-predictioncandidate list according in the order of uni-prediction motion vectors,L0 motion vector of bi-prediction motion vectors, L1 motion vector ofbi-prediction motion vectors, and averaged motion vector of the L0 andL1 motion vectors of bi-prediction motion vectors. If the number ofcandidates is less than five, zero motion vector is added to the list.

Adaptive Weighting Process

After predicting each triangular prediction unit, an adaptive weightingprocess is applied to the diagonal edge between the two triangularprediction units to derive the final prediction for the whole CU. Twoweighting factor groups are listed as follows:

-   -   1^(st) weighting factor group: {7/8, 6/8, 4/8, 2/8, 1/8} and        {7/8, 4/8, 1/8} are used for the luminance and the chrominance        samples, respectively;    -   2^(nd) weighting factor group: {7/8, 6/8, 5/8, 4/8, 3/8, 2/8,        1/8} and {6/8, 4/8, 2/8} are used for the luminance and the        chrominance samples, respectively.

One weighting factor group is selected based on the comparison of themotion vectors of two triangular prediction units. The 2nd weightingfactor group is used when the reference pictures of the two triangularprediction units are different from each other or their motion vectordifference is larger than 16 pixels. Otherwise, the Pt weighting factorgroup is used. An example is shown in FIG. 18 .

Motion Vector Storage

The motion vectors (Mv1 and Mv2 in FIG. 19 ) of the triangularprediction units are stored in 4×4 grids. For each 4×4 grid, eitheruni-prediction or bi-prediction motion vector is stored depending on theposition of the 4×4 grid in the CU. As shown in FIG. 19 , uni-predictionmotion vector, either Mv1 or Mv2, is stored for the 4×4 grid located inthe non-weighted area. On the other hand, a bi-prediction motion vectoris stored for the 4×4 grid located in the weighted area. Thebi-prediction motion vector is derived from Mv1 and Mv2 according to thefollowing rules:

-   -   1) In the case that Mv1 and Mv2 have motion vector from        different directions (L0 or L1), Mv1 and Mv2 are simply combined        to form the bi-prediction motion vector.    -   2) In the case that both Mv1 and Mv2 are from the same L0 (or        L1) direction,        -   2.a) If the reference picture of Mv2 is the same as a            picture in the L1 (or L0) reference picture list, Mv2 is            scaled to the picture. Mv1 and the scaled Mv2 are combined            to form the bi-prediction motion vector.        -   2.b) If the reference picture of Mv1 is the same as a            picture in the L1 (or L0) reference picture list, Mv1 is            scaled to the picture. The scaled Mv1 and Mv2 are combined            to form the bi-prediction motion vector.        -   2.c) Otherwise, only Mv1 is stored for the weighted area.

2.2.10. Affine Motion Compensation Prediction

In HEVC, only translation motion model is applied for motioncompensation prediction (MCP). While in the real world, there are manykinds of motion, e.g., zoom in/out, rotation, perspective motions andthe other irregular motions. In the JEM, a simplified affine transformmotion compensation prediction is applied. As shown in FIG. 20 , theaffine motion field of the block is described by two control pointmotion vectors.

The motion vector field (MVF) of a block is described by the followingequation:

$\begin{matrix}\{ \begin{matrix}{v_{x} = {{\frac{( {v_{1x} - v_{0x}} )}{w}x} - {\frac{( {v_{1y} - v_{0y}} )}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{( {v_{1y} - v_{0y}} )}{w}x} + {\frac{( {v_{1x} - v_{0x}} )}{w}y} + v_{0y}}}\end{matrix}  & {{Eq}.(6)}\end{matrix}$

Where (v_(0x), v_(0y)) is motion vector of the top-left corner controlpoint, and (v_(1x), v_(1y)) is motion vector of the top-right cornercontrol point.

In order to further simplify the motion compensation prediction,sub-block based affine transform prediction is applied. The sub-blocksize M×N is derived as in Eq. (7), where MvPre is the motion vectorfraction accuracy ( 1/16 in JEM), (v_(2x), v_(2y)) is motion vector ofthe bottom-left control point, calculated according to Eq. (6).

$\begin{matrix}\{ \begin{matrix}{M = {{clip}3( {4,w,\frac{w \times {MvPre}}{\max( {{{abs}( {v_{1x} - v_{0x}} )},{{abs}( {v_{1y} - v_{0y}} )}} )}} )}} \\{N = {{clip}3( {4,h,\frac{h \times {MvPre}}{\max( {{{abs}( {v_{2x} - v_{0x}} )},{{abs}( {v_{2y} - v_{0y}} )}} )}} )}}\end{matrix}  & {{Eq}.(7)}\end{matrix}$

After derived by Eq. (7), M and N should be adjusted downward ifnecessary to make it a divisor of w and h, respectively.

To derive motion vector of each M×N sub-block, the motion vector of thecenter sample of each sub-block, as shown in FIG. 21 , is calculatedaccording to Equation 1, and rounded to 1/16 fraction accuracy. Then themotion compensation interpolation filters mentioned in section 2.2.5 areapplied to generate the prediction of each sub-block with derived motionvector.

After MCP, the high accuracy motion vector of each sub-block is roundedand saved as the same accuracy as the normal motion vector.

2.2.10.1. AF_INTER Mode

In the JEM, there are two affine motion modes: AF_INTER mode andAF_MERGE mode. For CUs with both width and height larger than 8,AF_INTER mode can be applied. An affine flag in CU level is signalled inthe bitstream to indicate whether AF_INTER mode is used. In this mode, acandidate list with motion vector pair {(v₀, v₁)|v₀={v_(A), v_(B),v_(C)}, v₁={v_(D),v_(E)}} is constructed using the neighbour blocks. Asshown in FIG. 23 , v₀ is selected from the motion vectors of the blockA, B or C. The motion vector from the neighbour block is scaledaccording to the reference list and the relationship among the POC ofthe reference for the neighbour block, the POC of the reference for thecurrent CU and the POC of the current CU. And the approach to select v₁from the neighbour block D and E is similar. If the number of candidatelist is smaller than 2, the list is padded by the motion vector paircomposed by duplicating each of the AMVP candidates. When the candidatelist is larger than 2, the candidates are firstly sorted according tothe consistency of the neighboring motion vectors (similarity of the twomotion vectors in a pair candidate) and only the first two candidatesare kept. An RD cost check is used to determine which motion vector paircandidate is selected as the control point motion vector prediction(CPMVP) of the current CU. And an index indicating the position of theCPMVP in the candidate list is signalled in the bitstream. After theCPMVP of the current affine CU is determined, affine motion estimationis applied and the control point motion vector (CPMV) is found. Then thedifference of the CPMV and the CPMVP is signalled in the bitstream.

In AF_INTER mode, when 4/6 parameter affine mode is used, 2/3 controlpoints are required, and therefore 2/3 MVD needs to be coded for thesecontrol points, as shown in FIG. 22 . In JVET-K0337, it is proposed toderive the MV as follows, i.e., mvd₁ and mvd₂ are predicted from mvd₀.

mv₀=mv ₀+mvd ₀  Eq. (8)

mv₁=mv ₁+mvd ₁+mvd ₀  Eq. (9)

mv₂=mv ₂+mvd ₂+mvd ₀  Eq. (10)

Wherein mv _(i), mvd_(i) and mv₁ are the predicted motion vector, motionvector difference and motion vector of the top-left pixel (i=0),top-right pixel (i=1) or left-bottom pixel (i=2) respectively, as shownin FIG. 22 . Please note that the addition of two motion vectors (e.g.,mvA(xA, yA) and mvB(xB, yB)) is equal to summation of two componentsseparately, that is, newMV=mvA+mvB and the two components of newMV isset to (xA+xB) and (yA+yB), respectively.

2.2.10.2. Fast Affine ME Algorithm in AF_INTER Mode

In affine mode, MV of 2 or 3 control points needs to be determinedjointly. Directly searching the multiple MVs jointly is computationallycomplex. A fast affine ME algorithm is proposed and is adopted intoVTM/benchmark set (BMS).

The fast affine ME algorithm is described for the 4-parameter affinemodel, and the idea can be extended to 6-parameter affine model.

$\begin{matrix}\{ \begin{matrix}{x^{\prime} = {{ax} + {by} + c}} \\{y^{\prime} = {{- {bx}} + {ay} + d}}\end{matrix}  & {{Eq}.(11)}\end{matrix}$ $\begin{matrix}\{ \begin{matrix}{{mv}_{({x,y})}^{h} = {{x^{\prime} - x} = {{( {a - 1} )x} + {by} + c}}} \\{{mv}_{({x,y})}^{v} = {{y^{\prime} - y} = {{- {bx}} + {( {a - 1} )y} + d}}}\end{matrix}  & {{Eq}.(12)}\end{matrix}$

Replace (a−1) with a′, then the motion vector can be rewritten as:

$\begin{matrix}\{ \begin{matrix}{{mv}_{({x,y})}^{h} = {{x^{\prime} - x} = {{a^{\prime}x} + {by} + c}}} \\{{mv}_{({x,y})}^{v} = {{y^{\prime} - y} = {{- {bx}} + {a^{\prime}y} + d}}}\end{matrix}  & {{Eq}.(13)}\end{matrix}$

Suppose motion vectors of the two controls points (0, 0) and (0, w) areknown, from Equation (5) we can derive affine parameters,

$\begin{matrix}\{ \begin{matrix}{c = {mv}_{({0,0})}^{h}} \\{d = {mv}_{({0,0})}^{v}}\end{matrix}  & {{Eq}.(14)}\end{matrix}$

The motion vectors can be rewritten in vector form as:

$\begin{matrix}{{{MV}(p)} = {{A(p)}*{MV}_{C}^{T}}} & {{Eq}.(15)}\end{matrix}$ $\begin{matrix}{{{Wherein}{A(P)}} = \begin{bmatrix}1 & x & 0 & y \\0 & y & 1 & {- x}\end{bmatrix}} & {{Eq}.(16)}\end{matrix}$ $\begin{matrix}{{MV}_{C} = \lbrack {{mv}_{({0,0})}^{h}a{mv}_{({0,0})}^{v}b} \rbrack} & {{Eq}.(17)}\end{matrix}$

P=(x, y) is the pixel position.

At encoder, MVD of AF_INTER are derived iteratively. Denote MV^(i)(P) asthe MV derived in the ith iteration for position P and denote dMV_(C)^(i) as the delta updated for MV_(C) in the ith iteration. Then in the(i+1)th iteration,

$\begin{matrix}\begin{matrix}{{{MV}^{i + 1}(P)} = {{A(P)}*( {( {MV}_{C}^{i} )^{T} + ( {dMV}_{C}^{i} )^{T}} )}} \\{= {{{A(P)}*( {MV}_{C}^{i} )^{T}} + {{A(P)}*( {dMV}_{C}^{i} )^{T}}}} \\{= {{{MV}^{i}(P)} + {{A(P)}*( {dMV}_{C}^{i} )^{T}}}}\end{matrix} & {{Eq}.(18)}\end{matrix}$

Denote Pic_(ref) as the reference picture and denote Pic_(cur) as thecurrent picture and denote Q=P+MV^(i)(P). Suppose we use MSE as thematching criterion, then we need to minimize:

$\begin{matrix}{{\min{\sum\limits_{P}( {{{Pic}_{cur}(P)} - {{Pic}_{ref}( {P + {{MV}^{i + 1}(P)}} )}} )^{2}}} = {\min{\sum_{P}( {{{Pic}_{cur}(P)} - {{Pic}_{ref}( {Q + {{A(P)}*( {dMV}_{C}^{i} )^{T}}} )}} )^{2}}}} & {{Eq}.(19)}\end{matrix}$

Suppose (dMV_(C) ^(i))^(T) is small enough, we can rewrite Pic_(ref)(Q+A(P)*(dMV_(C) ^(i))^(T)) approximately as follows with lth orderTaylor expansion.

$\begin{matrix}{{{Pic}_{ref}( {Q + {{A(P)}*( {dMV}_{C}^{i} )^{T}}} )} \approx {{{Pic}_{ref}(Q)} + {{{Pic}_{ref}^{\prime}(Q)}*{A(P)}*( {dMV}_{C}^{i} )^{T}}}} & {{Eq}.(20)}\end{matrix}$${{{Wherein}{{Pic}_{ref}^{\prime}(Q)}} = {{{\lbrack {\frac{{dPic}_{ref}(Q)}{dx}\frac{{dPic}_{ref}(Q)}{dy}} \rbrack.{Denote}}{E^{i + 1}(P)}} = {{{Pic}_{cur}(P)} - {{Pic}_{ref}(Q)}}}},$$\begin{matrix}{{\min{\sum_{P}( {{{Pic}_{cur}(P)} - {{Pic}_{ref}(Q)} - {{{Pic}_{ref}^{\prime}(Q)}*{A(P)}*( {dMV}_{C}^{i} )^{T}}} )^{2}}} = {\min{\sum_{P}( {{E^{i + 1}(P)} - {{{Pic}_{ref}^{\prime}(Q)}*{A(P)}*( {dMV}_{C}^{i} )^{T}}} )^{2}}}} & {{Eq}.(21)}\end{matrix}$

we can derive dMV_(C) ^(i) by setting the derivative of the errorfunction to zero. Then can then calculate delta MV of the control points(0, 0) and (0, w) according to A(P)*(DMV_(C) ^(i))^(T),

dMV_((0,0)) ^(h) =dMV_(C) ^(i)[0]  Eq. (22)

dMV_((o,w)) ^(h) =dMV_(C) ^(i)[1]*w+dMV_(C) ^(i)[2]  Eq. (23)

dMV_((0,0)) ^(v) =dMV_(C) ^(i)[2]  Eq. (1)

dMV_((0,w)) ^(v) =−dMV_(C) ^(i)[3]*w+dMV_(C) ^(i)[2]  Eq. (25)

Suppose such MVD derivation process is iterated by n times, then thefinal MVD is calculated as follows,

fdMV_((0,0)) ^(h)=Σ_(i=0) ^(n-1) dMV_(C) ^(i)[0]  Eq. (2)

fdMV_((0,0)) ^(h)=Σ_(i=0) ^(n-1) dMV_(C) ^(i)[1]*w+Σ _(i=0) ^(n-1)dMV_(C) ^(i)[0]  Eq. (27)

fdMV_((0,0)) ^(v)=Σ_(i=0) ^(n-1) dMV_(C) ^(i)[2]  Eq. (3)

fdMV_((0,w)) ^(v)=Σ_(i=0) ^(n-1) dMV_(C) ^(i)[3]*w+Σ _(i=0) ^(n-1)dMV_(C) ^(i)[2]  Eq. (29)

With JVET-K0337, i.e., predicting delta MV of control point (0, w),denoted by mvd₁ from delta MV of control point (0, 0), denoted by mvd₀,now actually only (Σ_(i=0) ^(n-1)dMV_(C) ^(i)[1]*w, −Σ_(i=0)^(n-1)−dMV_(C) ^(i)[3]*w) is encoded for mvd₁.

2.2.10.3. AF_MERGE Mode

When a CU is applied in AF_MERGE mode, it gets the first block codedwith affine mode from the valid neighbour reconstructed blocks. And theselection order for the candidate block is from left, above, aboveright, left bottom to above left as shown in FIG. 24A, the motionvectors v₂, v₃ and v₄ of the top left corner, above right corner andleft bottom corner of the CU which contains the block A are derived. Andthe motion vector v₀ of the top left corner on the current CU iscalculated according to v₂, v₃ and v₄. Secondly, the motion vector v₁ ofthe above right of the current CU is calculated.

After the CPMV of the current CU v₀ and v₁ are derived, according to thesimplified affine motion model Equation 1, the MVF of the current CU isgenerated. In order to identify whether the current CU is coded withAF_MERGE mode, an affine flag is signalled in the bitstream when thereis at least one neighbour block is coded in affine mode.

FIGS. 24A and 24B show examples of candidates for AF_MERGE

In JVET-L0366, which was planned to be adopted into VTM 3.0, an affinemerge candidate list is constructed with following steps:

1) Insert Inherited Affine Candidates

Inherited affine candidate means that the candidate is derived from theaffine motion model of its valid neighbor affine coded block. In thecommon base, as shown in FIG. 25 , the scan order for the candidatepositions is: A1, B1, B0, A0 and B2.

After a candidate is derived, full pruning process is performed to checkwhether same candidate has been inserted into the list. If a samecandidate exists, the derived candidate is discarded.

2) Insert Constructed Affine Candidates

If the number of candidates in affine merge candidate list is less thanMaxNumAffineCand (set to 5 in this contribution), constructed affinecandidates are inserted into the candidate list. Constructed affinecandidate means the candidate is constructed by combining the neighbormotion information of each control point.

The motion information for the control points is derived firstly fromthe specified spatial neighbors and temporal neighbor shown in FIG. 25 .CPk (k=1, 2, 3, 4) represents the k-th control point. A0, A1, A2, B0,B1, B2 and B3 are spatial positions for predicting CPk (k=1, 2, 3); T istemporal position for predicting CP4.

The coordinates of CP1, CP2, CP3 and CP4 is (0, 0), (W, 0), (H, 0) and(W, H), respectively, where W and H are the width and height of currentblock.

The motion information of each control point is obtained according tothe following priority order:

For CP1, the checking priority is B2->B3->A2. B2 is used if it isavailable. Otherwise, if B2 is available, B3 is used. If both B2 and B3are unavailable, A2 is used. If all the three candidates areunavailable, the motion information of CP1 cannot be obtained.

For CP2, the checking priority is B1->B0.

For CP3, the checking priority is A1->A0.

For CP4, T is used.

Secondly, the combinations of controls points are used to construct anaffine merge candidate.

Motion information of three control points are needed to construct a6-parameter affine candidate. The three control points can be selectedfrom one of the following four combinations ({CP1, CP2, CP4}, {CP1, CP2,CP3}, {CP2, CP3, CP4}, {CP1, CP3, CP4}). Combinations {CP1, CP2, CP3},{CP2, CP3, CP4}, {CP1, CP3, CP4} will be converted to a 6-parametermotion model represented by top-left, top-right and bottom-left controlpoints.

Motion information of two control points are needed to construct a4-parameter affine candidate. The two control points can be selectedfrom one of the following six combinations ({CP1, CP4}, {CP2, CP3},{CP1, CP2}, {CP2, CP4}, {CP1, CP3}, {CP3, CP4}). Combinations {CP1,CP4}, {CP2, CP3}, {CP2, CP4}, {CP1, CP3}, {CP3, CP4} will be convertedto a 4-parameter motion model represented by top-left and top-rightcontrol points.

The combinations of constructed affine candidates are inserted into tocandidate list as following order: {CP1, CP2, CP3}, {CP1, CP2, CP4},{CP1, CP3, CP4}, {CP2, CP3, CP4}, {CP1, CP2}, {CP1, CP3}, {CP2, CP3},{CP1, CP4}, {CP2, CP4}, {CP3, CP4}

For reference list X (X being 0 or 1) of a combination, the referenceindex with highest usage ratio in the control points is selected as thereference index of list X, and motion vectors point to differencereference picture will be scaled.

After a candidate is derived, full pruning process is performed to checkwhether same candidate has been inserted into the list. If a samecandidate exists, the derived candidate is discarded.

3) Padding with Zero Motion Vectors

If the number of candidates in affine merge candidate list is less than5, zero motion vectors with zero reference indices are insert into thecandidate list, until the list is full.

2.2.11. Pattern Matched Motion Vector Derivation

Pattern matched motion vector derivation (PMMVD) mode is a special mergemode based on Frame-Rate Up Conversion (FRUC) techniques. With thismode, motion information of a block is not signalled but derived atdecoder side.

A FRUC flag is signalled for a CU when its merge flag is true. When theFRUC flag is false, a merge index is signalled and the regular mergemode is used. When the FRUC flag is true, an additional FRUC mode flagis signalled to indicate which method (bilateral matching or templatematching) is to be used to derive motion information for the block.

At encoder side, the decision on whether using FRUC merge mode for a CUis based on RD cost selection as done for normal merge candidate. Thatis the two matching modes (bilateral matching and template matching) areboth checked for a CU by using RD cost selection. The one leading to theminimal cost is further compared to other CU modes. If a FRUC matchingmode is the most efficient one, FRUC flag is set to true for the CU andthe related matching mode is used.

Motion derivation process in FRUC merge mode has two steps. A CU-levelmotion search is first performed, then followed by a Sub-CU level motionrefinement. At CU level, an initial motion vector is derived for thewhole CU based on bilateral matching or template matching. First, a listof MV candidates is generated and the candidate which leads to theminimum matching cost is selected as the starting point for further CUlevel refinement. Then a local search based on bilateral matching ortemplate matching around the starting point is performed and the MVresults in the minimum matching cost is taken as the MV for the wholeCU. Subsequently, the motion information is further refined at sub-CUlevel with the derived CU motion vectors as the starting points.

For example, the following derivation process is performed for a W×H CUmotion information derivation. At the first stage, MV for the whole W×HCU is derived. At the second stage, the CU is further split into M×Msub-CUs. The value of M is calculated as in (16), D is a predefinedsplitting depth which is set to 3 by default in the JEM. Then the MV foreach sub-CU is derived.

$\begin{matrix}{M = {\max\{ {4,{\min\{ {\frac{M}{2^{D}},\frac{N}{2^{D}}} \}}} \}}} & {{Eq}.(30)}\end{matrix}$

As shown in the FIG. 26 , the bilateral matching is used to derivemotion information of the current CU by finding the closest matchbetween two blocks along the motion trajectory of the current CU in twodifferent reference pictures. Under the assumption of continuous motiontrajectory, the motion vectors MV0 and MV1 pointing to the two referenceblocks shall be proportional to the temporal distances, i.e., TD0 andTD1, between the current picture and the two reference pictures. As aspecial case, when the current picture is temporally between the tworeference pictures and the temporal distance from the current picture tothe two reference pictures is the same, the bilateral matching becomesmirror based bi-directional MV.

As shown in FIG. 27 , template matching is used to derive motioninformation of the current CU by finding the closest match between atemplate (top and/or left neighboring blocks of the current CU) in thecurrent picture and a block (same size to the template) in a referencepicture. Except the aforementioned FRUC merge mode, the templatematching is also applied to AMVP mode. In the JEM, as done in HEVC, AMVPhas two candidates. With template matching method, a new candidate isderived. If the newly derived candidate by template matching isdifferent to the first existing AMVP candidate, it is inserted at thevery beginning of the AMVP candidate list and then the list size is setto two (meaning remove the second existing AMVP candidate). When appliedto AMVP mode, only CU level search is applied.

2.2.11.1. CU Level MV Candidate Set

The MV candidate set at CU level consists of:

-   -   (i) Original AMVP candidates if the current CU is in AMVP mode    -   (ii) all merge candidates,    -   (iii) several MVs in the interpolated MV field, which is        introduced in section 2.2.11.3.    -   (iv) top and left neighboring motion vectors

When using bilateral matching, each valid MV of a merge candidate isused as an input to generate a MV pair with the assumption of bilateralmatching. For example, one valid MV of a merge candidate is (MVa, refa)at reference list A. Then the reference picture refb of its pairedbilateral MV is found in the other reference list B so that refa andrefb are temporally at different sides of the current picture. If such arefb is not available in reference list B, refb is determined as areference which is different from refa and its temporal distance to thecurrent picture is the minimal one in list B. After refb is determined,MVb is derived by scaling MVa based on the temporal distance between thecurrent picture and refa, refb.

Four MVs from the interpolated MV field are also added to the CU levelcandidate list. More specifically, the interpolated MVs at the position(0, 0), (W/2, 0), (0, H/2) and (W/2, H/2) of the current CU are added.

When FRUC is applied in AMVP mode, the original AMVP candidates are alsoadded to CU level MV candidate set.

At the CU level, up to 15 MVs for AMVP CUs and up to 13 MVs for mergeCUs are added to the candidate list.

2.2.11.2. Sub-CU Level MV Candidate Set

The MV candidate set at sub-CU level consists of:

-   -   (i) an MV determined from a CU-level search,    -   (ii) top, left, top-left and top-right neighboring MVs,    -   (iii) scaled versions of collocated MVs from reference pictures,    -   (iv) up to 4 ATMVP candidates,    -   (v) up to 4 STMVP candidates

The scaled MVs from reference pictures are derived as follows. All thereference pictures in both lists are traversed. The MVs at a collocatedposition of the sub-CU in a reference picture are scaled to thereference of the starting CU-level MV.

ATMVP and STMVP candidates are limited to the four first ones.

At the sub-CU level, up to 17 MVs are added to the candidate list.

2.2.11.3. Generation of Interpolated MV Field

Before coding a frame, interpolated motion field is generated for thewhole picture based on unilateral ME. Then the motion field may be usedlater as CU level or sub-CU level MV candidates.

First, the motion field of each reference pictures in both referencelists is traversed at 4×4 block level. For each 4×4 block, if the motionassociated to the block passing through a 4×4 block in the currentpicture (as shown in FIG. 28 ) and the block has not been assigned anyinterpolated motion, the motion of the reference block is scaled to thecurrent picture according to the temporal distance TD0 and TD1 (the sameway as that of MV scaling of TMVP in HEVC) and the scaled motion isassigned to the block in the current frame. If no scaled MV is assignedto a 4×4 block, the block's motion is marked as unavailable in theinterpolated motion field.

2.2.11.4. Interpolation and Matching Cost

When a motion vector points to a fractional sample position, motioncompensated interpolation is needed. To reduce complexity, bi-linearinterpolation instead of regular 8-tap HEVC interpolation is used forboth bilateral matching and template matching.

The calculation of matching cost is a bit different at different steps.When selecting the candidate from the candidate set at the CU level, thematching cost is the absolute sum difference (SAD) of bilateral matchingor template matching. After the starting MV is determined, the matchingcost C of bilateral matching at sub-CU level search is calculated asfollows:

C=SAD+w·(|MV_(x)−MV_(x) ^(s)|+|MV_(y) −M _(y) ^(s)|)  Eq. (31)

where w is a weighting factor which is empirically set to 4, MV andMV^(s) indicate the current MV and the starting MV, respectively. SAD isstill used as the matching cost of template matching at sub-CU levelsearch.

In FRUC mode, MV is derived by using luma samples only. The derivedmotion will be used for both luma and chroma for MC inter prediction.After MV is decided, final MC is performed using 8-taps interpolationfilter for luma and 4-taps interpolation filter for chroma.

2.2.11.5. MV Refinement

MV refinement is a pattern based MV search with the criterion ofbilateral matching cost or template matching cost. In the JEM, twosearch patterns are supported—an unrestricted center-biased diamondsearch (UCBDS) and an adaptive cross search for MV refinement at the CUlevel and sub-CU level, respectively. For both CU and sub-CU level MVrefinement, the MV is directly searched at quarter luma sample MVaccuracy, and this is followed by one-eighth luma sample MV refinement.The search range of MV refinement for the CU and sub-CU step are setequal to 8 luma samples.

2.2.11.6. Selection of Prediction Direction in Template Matching FRUCMerge Mode

In the bilateral matching merge mode, bi-prediction is always appliedsince the motion information of a CU is derived based on the closestmatch between two blocks along the motion trajectory of the current CUin two different reference pictures. There is no such limitation for thetemplate matching merge mode. In the template matching merge mode, theencoder can choose among uni-prediction from list0, uni-prediction fromlist1 or bi-prediction for a CU. The selection is based on a templatematching cost as follows:

If costBi < = factor * min (cost0, cost1)  bi-prediction is used;Otherwise, if cost0 <= cost1  uni-prediction from list0 is used;Otherwise,  uni-prediction from list1 is used;

where cost0 is the SAD of list0 template matching, cost1 is the SAD oflist1 template matching and costBi is the SAD of bi-prediction templatematching. The value of factor is equal to 1.25, which means that theselection process is biased toward bi-prediction.

The inter prediction direction selection is only applied to the CU-leveltemplate matching process.

2.2.12. Generalized Bi-Prediction

In conventional bi-prediction, the predictors from L0 and L1 areaveraged to generate the final predictor using the equal weight 0.5. Thepredictor generation formula is shown as in Eq. (32)

P _(TraditionalBiPred)=(P _(L0) +P _(L1) Rounding Offset)>>shiftNum  Eq.(32)

In Eq. (32), P_(TraditionalBiPred) is the final predictor for theconventional bi-prediction, P_(L0) and P_(L1) are predictors from L0 andL1, respectively, and RoundingOffset and shiftNum are used to normalizethe final predictor.

Generalized Bi-prediction (GBI) is proposed to allow applying differentweights to predictors from L0 and L1. The predictor generation is shownin Eq. (32).

P _(GBi)=(1−w ₁)*P _(L0) +w ₁ *P_(L1)+RoundingOffset_(GBi))>>shiftNum_(GBi),  Eq. (33)

In Eq. (33), P_(GBi) is the final predictor of GBi. (1−w₁) and w₁ arethe selected GBI weights applied to the predictors of L0 and L1,respectively. RoundingOffset_(GBi) and shiftNum_(GBi) are used tonormalize the final predictor in GBi.

The supported weights of w₁ is {−1/4, 3/8, 1/2, 5/8, 5/4}. Oneequal-weight set and four unequal-weight sets are supported. For theequal-weight case, the process to generate the final predictor isexactly the same as that in the conventional bi-prediction mode. For thetrue bi-prediction cases in random access (RA) condition, the number ofcandidate weight sets is reduced to three.

For advanced motion vector prediction (AMVP) mode, the weight selectionin GBI is explicitly signaled at CU-level if this CU is coded bybi-prediction. For merge mode, the weight selection is inherited fromthe merge candidate. In this proposal, GBI supports DMVR to generate theweighted average of template as well as the final predictor for BMS-1.0.

2.2.13. Multi-Hypothesis Inter Prediction

In the multi-hypothesis inter prediction mode, one or more additionalprediction signals are signaled, in addition to the conventional uni/biprediction signal. The resulting overall prediction signal is obtainedby sample-wise weighted superposition. With the uni/bi prediction signalp_(uni/bi) and the first additional inter prediction signal/hypothesish₃, the resulting prediction signal p₃ is obtained as follows:

p ₃=(1−α)P _(uni/bi) +αh ₃  Eq. (34)

The changes to the prediction unit syntax structure are shown as boldtext in the table below:

TABLE 2 prediction_unit( x0, y0, nPbW, nPbH ) { Descriptor  ...  if( !cu_skip_flag[ x0 ][ y0 ] ) {   i = 0   readMore = 1   while( i <MaxNumAdditionalHypotheses && readMore )   {   additional_hypothesis_flag[ x0 ][ y0 ][ i ] ae(v)    if(additional_hypothesis_flag[ x0 ][ y0 ][ i ] ) {     ref_idx_add_hyp[ x0][ y0 ][ i ] ae(v)     mvd_coding( x0, y0, 2+i )     mvp_add_hyp_flag[x0 ][ y0 ][ i ] ae(v)     add_hyp_weight_idx[ x0 ][ y0 ][ i ] ae(v)    }   readMore = additional_hypothesis_flag[ x0 ][ y0 ][ i ]    i++   }  }}

The weighting factor a is specified by the syntax elementadd_hyp_weight_idx, according to the following mapping:

TABLE 3 add_hyp_weight_idx α 0   ¼ 1 −⅛

Note that for the additional prediction signals, the concept ofprediction list0/list1 is abolished, and instead one combined list isused. This combined list is generated by alternatingly insertingreference frames from list0 and list1 with increasing reference index,omitting reference frames which have already been inserted, such thatdouble entries are avoided.

Analogously to above, more than one additional prediction signals can beused. The resulting overall prediction signal is accumulated iterativelywith each additional prediction signal.

P _(n+1)=(1−α_(n+1))p _(n)+α_(n+1) h _(n+1)  Eq. (35)

The resulting overall prediction signal is obtained as the last p_(n)(i.e., the p_(n) having the largest index n).

Note that also for inter prediction blocks using MERGE mode (but notSKIP mode), additional inter prediction signals can be specified.Further note, that in case of MERGE, not only the uni/bi predictionparameters, but also the additional prediction parameters of theselected merging candidate can be used for the current block.

2.2.14. Multi-Hypothesis Prediction for Uni-Prediction of AMVP Mode

When the multi-hypothesis prediction is applied to improveuni-prediction of AMVP mode, one flag is signaled to enable or disablemulti-hypothesis prediction for inter_dir equal to 1 or 2, where 1, 2,and 3 represent list 0, list 1, and bi-prediction, respectively.Moreover, one more merge index is signaled when the flag is true. Inthis way, multi-hypothesis prediction turns uni-prediction intobi-prediction, where one motion is acquired using the original syntaxelements in AMVP mode while the other is acquired using the mergescheme. The final prediction uses 1:1 weights to combine these twopredictions as in bi-prediction. The merge candidate list is firstderived from merge mode with sub-CU candidates (e.g., affine,alternative temporal motion vector prediction (ATMVP)) excluded. Next,it is separated into two individual lists, one for list 0 (L0)containing all L0 motions from the candidates, and the other for list 1(L1) containing all L1 motions. After removing redundancy and fillingvacancy, two merge lists are generated for L0 and L1 respectively. Thereare two constraints when applying multi-hypothesis prediction forimproving AMVP mode. First, it is enabled for those CUs with the lumacoding block (CB) area larger than or equal to 64. Second, it is onlyapplied to L1 when in low delay B pictures.

2.2.15. Multi-Hypothesis Prediction for Skip/Merge Mode

When the multi-hypothesis prediction is applied to skip or merge mode,whether to enable multi-hypothesis prediction is explicitly signaled. Anextra merge indexed prediction is selected in addition to the originalone. Therefore, each candidate of multi-hypothesis prediction implies apair of merge candidates, containing one for the 1^(st) merge indexedprediction and the other for the 2^(nd) merge indexed prediction.However, in each pair, the merge candidate for the 2^(nd) merge indexedprediction is implicitly derived as the succeeding merge candidate(i.e., the already signaled merge index plus one) without signaling anyadditional merge index. After removing redundancy by excluding thosepairs, containing similar merge candidates and filling vacancy, thecandidate list for multi-hypothesis prediction is formed. Then, motionsfrom a pair of two merge candidates are acquired to generate the finalprediction, where 5:3 weights are applied to the 1^(st) and 2^(nd) mergeindexed predictions, respectively. Moreover, a merge or skip CU withmulti-hypothesis prediction enabled can save the motion information ofthe additional hypotheses for reference of the following neighboring CUsin addition to the motion information of the existing hypotheses. Notethat sub-CU candidates (e.g., affine, ATMVP) are excluded from thecandidate list, and for low delay B pictures, multi-hypothesisprediction is not applied to skip mode. Moreover, when multi-hypothesisprediction is applied to merge or skip mode, for those CUs with CU widthor CU height less than 16, or those CUs with both CU width and CU heightequal to 16, bi-linear interpolation filter is used in motioncompensation for multiple hypotheses. Therefore, the worst-casebandwidth (required access samples per sample) for each merge or skip CUwith multi-hypothesis prediction enabled is calculated in Table 1 andeach number is less than half of the worst-case bandwidth for each 4×4CU with multi-hypothesis prediction disabled.

2.2.16. Ultimate Motion Vector Expression

Ultimate motion vector expression (UMVE) is presented. UMVE is used foreither skip or merge modes with a proposed motion vector expressionmethod.

UMVE re-uses merge candidate as same as using in VVC. Among the mergecandidates, a candidate can be selected, and is further expanded by theproposed motion vector expression method.

UMVE provides a new motion vector expression with simplified signaling.The expression method includes starting point, motion magnitude, andmotion direction.

FIG. 29 shows an example of UMVE Search Process

FIG. 30 shows examples of UMVE Search Points.

This proposed technique uses a merge candidate list as it is. But onlycandidates which are default merge type (MRG_TYPE_DEFAULT_N) areconsidered for UMVE's expansion.

Base candidate index defines the starting point. Base candidate indexindicates the best candidate among candidates in the list as follows.

TABLE 4 Base candidate IDX Base candidate IDX 0 1 2 3 N^(th) MVP 1^(st)MVP 2^(nd) MVP 3^(rd) MVP 4^(th) MVP

If the number of base candidate is equal to 1, Base candidate IDX is notsignaled.

Distance index is motion magnitude information. Distance index indicatesthe pre-defined distance from the starting point information.Pre-defined distance is as follows:

TABLE 5 Distance IDX Distance IDX 0 1 2 3 4 5 6 7 Pixel ¼-pel ½-pel1-pel 2-pel 4-pel 8-pel 16-pel 32-pel dis- tance

Direction index represents the direction of the MVD relative to thestarting point. The direction index can represent of the four directionsas shown below.

TABLE 6 Direction IDX Direction IDX 00 01 10 11 x-axis + − N/A N/Ay-axis N/A N/A + −

UMVE flag is signaled right after sending a skip flag and merge flag. Ifskip and merge flag is true, UMVE flag is parsed. If UMVE flag is equalto 1, UMVE syntaxes are parsed. But, if not 1, AFFINE flag is parsed. IfAFFINE flag is equal to 1, that is AFFINE mode, But, if not 1,skip/merge index is parsed for VTM's skip/merge mode.

Additional line buffer due to UMVE candidates is not needed. Because askip/merge candidate of software is directly used as a base candidate.Using input UMVE index, the supplement of MV is decided right beforemotion compensation. There is no need to hold long line buffer for this.

2.2.17. Affine Merge Mode with Prediction Offsets

UMVE is extended to affine merge mode, which will be referred to as UMVEaffine mode thereafter. The proposed method selects the first availableaffine merge candidate as a base predictor. Then it applies a motionvector offset to each control point's motion vector value from the basepredictor. If there's no affine merge candidate available, this proposedmethod will not be used.

The selected base predictor's inter prediction direction, and thereference index of each direction is used without change.

In the current implementation, the current block's affine model isassumed to be a 4-parameter model, only 2 control points need to bederived. Thus, only the first 2 control points of the base predictorwill be used as control point predictors.

For each control point, a zero_MVD flag is used to indicate whether thecontrol point of current block has the same MV value as thecorresponding control point predictor. If zero_MVD flag is true, there'sno other signaling needed for the control point. Otherwise, a distanceindex and an offset direction index is signaled for the control point.

A distance offset table with size of 5 is used as shown in the tablebelow. Distance index is signaled to indicate which distance offset touse. The mapping of distance index and distance offset values is shownin FIG. 30 .

TABLE 7 Distance offset table Distance IDX 0 1 2 3 4 Distance-offset½-pel 1-pel 2-pel 4-pel 8-pel

FIG. 31 shows an example of distance index and distance offset mapping.

The direction index can represent four directions as shown below, whereonly x or y direction may have an MV difference, but not in bothdirections.

TABLE 8 Offset direction table Offset Direction IDX 00 01 10 11x-dir-factor +1 −1 0 0 y-dir-factor 0 0 +1 −1

If the inter prediction is uni-directional, the signaled distance offsetis applied on the offset direction for each control point predictor.Results will be the MV value of each control point.

For example, when base predictor is uni-directional, and the motionvector values of a control point is MVP (v_(px), v_(py)). When distanceoffset and direction index are signaled, the motion vectors of currentblock's corresponding control points will be calculated as below.

MV(v _(x) ,v _(y))=MVP(v _(px) ,v_(py))+MV(x-dir-factor*distance-offset,y-dir-factor*distance-offset)  Eq.(36)

If the inter prediction is bi-directional, the signaled distance offsetis applied on the signaled offset direction for control pointpredictor's L0 motion vector; and the same distance offset with oppositedirection is applied for control point predictor's L1 motion vector.Results will be the MV values of each control point, on each interprediction direction.

For example, when base predictor is uni-directional, and the motionvector values of a control point on L0 is MVP_(L0) (v_(0px), v_(0py)),and the motion vector of that control point on L1 is MVP_(L1) (v_(1px),v_(1py)). When distance offset and direction index are signaled, themotion vectors of current block's corresponding control points will becalculated as below.

MV_(L0)(v _(0x) ,v _(0y))=MVP_(L0)(v _(0px) ,v_(0py))+MV(x-dir-factor*distance-offset,y-dir-factor*distance-offset)  Eq. (37)

MV_(L1)(v _(0x) ,v _(0y))=MVP_(L1)(v _(0px) ,v_(0py))+MV(−x-dir-factor*distance-offset,−y-dir-factor*distance-offset)  Eq. (38)

2.2.18. Bi-Directional Optical Flow

Bi-directional Optical flow (BIO) is sample-wise motion refinement whichis performed on top of block-wise motion compensation for bi-prediction.The sample-level motion refinement doesn't use signalling.

Let I^((k)) be the luma value from reference k (k=0, 1) after blockmotion compensation, and ∂I^((k))/∂x, ∂I/∂y are horizontal and verticalcomponents of the I^((k)) gradient, respectively. Assuming the opticalflow is valid, the motion vector field (v_(x), v_(y)) is given by anequation:

∂I ^((k)) /∂t+v _(x) ∂I(k)/∂x+v _(y) ∂I ^((k)) /∂y=0.  Eq. (4)

Combining this optical flow equation with Hermite interpolation for themotion trajectory of each sample results in a unique third-orderpolynomial that matches both the function values I^((k)) and derivatives∂I^((k))/∂x, ∂I^((k))/∂y at the ends. The value of this polynomial att=0 is the BIO prediction:

pred_(BIO)=)1/2·(I ⁽⁰⁾ +I ⁽¹⁾ +v _(x)/2·(τ₁ ∂I ⁽¹⁾ /∂x−τ ₀ ∂I ⁽⁰⁾ /∂x)+v_(y)/2·(τ₁ ∂I ⁽¹⁾ /∂y−τ ₀ ∂I ⁽⁰⁾ /∂y))  Eq.(5)

Here, τ₀ and τ₁ denote the distances to the reference frames as shown inFIG. 31 . Distances τ₀ and τ₁ are calculated based on POC for Ref0 andRef1: τ₀=POC(current)−POC(Ref0), τ₁=POC(Ref1)−POC(current). If bothpredictions come from the same time direction (either both from the pastor both from the future) then the signs are different (i.e., τ₀·τ₁<0).In this case, BIO is applied only if the prediction is not from the sametime moment (i.e., τ₀≠τ₁), both referenced regions have non-zero motion(MVx₀,MVy₀,MVx₁,MVy₁≠0) and the block motion vectors are proportional tothe time distance (MVx₀/MVx₁=MVy₀/MVY₁=−τ₀/τ₁).

The motion vector field (v_(x), v_(y)) is determined by minimizing thedifference Δ between values in points A and B (intersection of motiontrajectory and reference frame planes on FIG. 32 ). Model uses onlyfirst linear term of a local Taylor expansion for A:

Δ=(I ⁽⁰⁾ −I ⁽¹⁾ ₀ +v _(x)(τ₁ ∂I ⁽¹⁾ /∂x+τ ₀ ∂I ⁽⁰⁾ /∂x)+v _(y)(τ₁ /∂I⁽¹⁾ /∂y)+τ₀ ∂I ⁽⁰⁾ /∂y))   Eq. (41)

All values in Eq. (41) depend on the sample location (i′, j′), which wasomitted from the notation so far. Assuming the motion is consistent inthe local surrounding area, we minimize Δ inside the (2M+1)×(2M+1)square window Ω centered on the currently predicted point (i, j), whereM is equal to 2:

$\begin{matrix}{( {v_{x},v_{y}} ) = {\underset{v_{x},v_{y}}{\arg\min}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\Delta^{2}\lbrack {i^{\prime},j^{\prime}} \rbrack}}}} & {{Eq}.(42)}\end{matrix}$

For this optimization problem, the JEM uses a simplified approach makingfirst a minimization in the vertical direction and then in thehorizontal direction. This results in:

$\begin{matrix}{v_{x} = {( {s_{1} + r} ) > {{m?{clip}}3( {{- {thBIO}},{thBIO},{- \frac{s_{3}}{( {s_{1} + r} )}}} ):0}}} & {{Eq}.(43)}\end{matrix}$ $\begin{matrix}{{v_{y} = {( {s_{5} + r} ) > {{m?{clip}}3( {{- {thBIO}},{thBIO},{- \frac{s_{6} + {v_{x}{s_{2}/2}}}{( {s_{5} + r} )}}} ):0{where}}}},} & {{Eq}.(44)}\end{matrix}$ $\begin{matrix}{{s_{1} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}( {{\tau_{1}{\partial I^{(1)}}/{\partial x}} + {\tau_{0}{\partial I^{(0)}}/{\partial x}}} )^{2}}};{s_{3} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{( {I^{(1)} - I^{(0)}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial x}} + {\tau_{0}{\partial I^{(0)}}/{\partial x}}} )}}};} & {{Eq}.(6)}\end{matrix}$${s_{2} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{( {{\tau_{1}{\partial I^{(1)}}/{\partial x}} + {\tau_{0}{\partial I^{(0)}}/{\partial x}}} )( {{\tau_{1}{\partial I^{(1)}}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )}}};$${s_{5} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}( {{\tau_{1}/{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )^{2}}};{s_{6} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{( {I^{(1)} - I^{(0)}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )}}}$

In order to avoid division by zero or a very small value, regularizationparameters r and m are introduced in Eq. (43) and Eq. (44).

r=500·4^(d-8)  Eq. (46)

m=700·4^(d-8)  Eq.(47)

Here d is bit depth of the video samples.

In order to keep the memory access for BIO the same as for regularbi-predictive motion compensation, all prediction and gradients values,I^((k)), ∂I^((k))/∂x, ∂I^((k))/∂y, are calculated only for positionsinside the current block. In Equation 30, (2M+1)×(2M+1) square window Ωcentered in currently predicted point on a boundary of predicted blockneeds to accesses positions outside of the block (as shown in FIG. 33A).In the JEM, values of I^((k)), ∂I^((k))/∂x, ∂I^((k))/∂y outside of theblock are set to be equal to the nearest available value inside theblock. For example, this can be implemented as padding, as shown in FIG.33B.

With BIO, it's possible that the motion field can be refined for eachsample. To reduce the computational complexity, a block-based design ofBIO is used in the JEM. The motion refinement is calculated based on 4×4block. In the block-based BIO, the values of s_(n) in Equation 30 of allsamples in a 4×4 block are aggregated, and then the aggregated values ofs_(n) in are used to derived BIO motion vectors offset for the 4×4block. More specifically, the following formula is used for block-basedBIO derivation:

$\begin{matrix}{{s_{1,b_{k}} = {\sum_{{({x,y})} \in b_{k}}{\sum_{{\lbrack{i^{\prime},j}\rbrack} \in {\square({x,y})}}( {{\tau_{1}{\partial I^{(1)}}/{\partial x}} + {\tau_{0}{\partial I^{(0)}}/{\partial x}}} )^{2}}}};{s_{3,b_{k}} = {\sum_{{({x,y})} \in b_{k}}{\sum_{{\lbrack{i^{\prime},j}\rbrack} \in \square}{( {I^{(1)} - I^{(0)}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial x}} + {\tau_{0}{\partial I^{(0)}}/{\partial x}}} )}}}};{s_{2,b_{x}} = {\sum_{{({x,y})} \in b_{k}}{\sum_{{\lbrack{i^{\prime},j}\rbrack} \in \square}{( {{\tau_{1}{\partial I^{(1)}}/{\partial x}} + {\tau_{0}{\partial I^{(0)}}/{\partial x}}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )}}}};{s_{5,{b_{k} =}}{\sum_{{({x,y})} \in b_{k}}{\sum_{{\lbrack{i^{\prime},j}\rbrack} \in \square}( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )^{2}}}};{s_{6,b_{k}} = {\sum_{{({x,y})} \in b_{k}}{\sum_{{\lbrack{i^{\prime},j}\rbrack} \in \square}{( {I^{(1)} - I^{(0)}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )}}}}} & {{Eq}.(48)}\end{matrix}$${s_{5,{b_{k} =}}{\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \square}( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )^{2}}}};{s_{6,{b_{k} =}}{\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \square}{( {I^{(1)} - I^{(0)}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )}}}}$${s_{5,{b_{k} =}}{\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \square}( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )^{2}}}};{s_{6,{b_{k} =}}{\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \square}{( {I^{(1)} - I^{(0)}} )( {{\tau_{1}{\partial I^{(1)}}/{\partial y}} + {\tau_{0}{\partial I^{(0)}}/{\partial y}}} )}}}}$

where b_(k) denotes the set of samples belonging to the k-th 4×4 blockof the predicted block. s_(n) in Eq. (43) and Eq. (44) are replaced by((s_(n,bk))>>4) to derive the associated motion vector offsets.

In some cases, MV regiment of BIO might be unreliable due to noise orirregular motion. Therefore, in BIO, the magnitude of MV regiment isclipped to a threshold value thBIO. The threshold value is determinedbased on whether the reference pictures of the current picture are allfrom one direction. If all the reference pictures of the current pictureare from one direction, the value of the threshold is set to12×2^(14-d); otherwise, it is set to 12×2^(13-d).

Gradients for BIO are calculated at the same time with motioncompensation interpolation using operations consistent with HEVC motioncompensation process (2D separable FIR). The input for this 2D separableFIR is the same reference frame sample as for motion compensationprocess and fractional position (fracX, fracY) according to thefractional part of block motion vector. In case of horizontal gradient∂I/∂x signal first interpolated vertically using BIOfilterScorresponding to the fractional position fracY with de-scaling shiftd-8, then gradient filter BIOfilterG is applied in horizontal directioncorresponding to the fractional position fracX with de-scaling shift by18-d. In case of vertical gradient ∂I/∂y first gradient filter isapplied vertically using BIOfilterG corresponding to the fractionalposition fracY with de-scaling shift d-8, then signal displacement isperformed using BIOfilterS in horizontal direction corresponding to thefractional position fracX with de-scaling shift by 18-d. The length ofinterpolation filter for gradients calculation BIOfilterG and signaldisplacement BIOfilterF is shorter (6-tap) in order to maintainreasonable complexity. Table 9:9 shows the filters used for gradientscalculation for different fractional positions of block motion vector inBIO. Table 10: 10 shows the interpolation filters used for predictionsignal generation in BIO.

TABLE 9 Filters for gradients calculation in BIO Interpolation filterfor Fractional pel position gradient(BIOfilterG) 0 {   8, −39,  −3, 46,−17, 5} 1/16 {   8, −32, −13, 50, −18, 5} ⅛ {   7, −27, −20, 54, −19, 5}3/16 {   6, −21, −29, 57, −18, 5} ¼ {   4, −17, −36, 60, −15, 4} 5/16 {  3,  −9, −44, 61, −15, 4} ⅜ {   1,  −4, −48, 61, −13, 3} 7/16 {   0,   1, −54, 60,  −9, 2} ½ { −1,    4, −57, 57,  −4, 1}

TABLE 10 Interpolation filters for prediction signal gneration in BIOInterpolation filter for Fractional pel position predictionsignal(BIOfilterS) 0 { 0,    0, 64,  0,    0, 0} 1/16 { 1,  −3, 64,  4, −2, 0} ⅛ { 1,  −6, 62,  9,  −3, 1} 3/16 { 2,  −8, 60, 14,  −5, 1} ¼ {2,  −9, 57, 19,  −7, 2} 5/16 { 3, −10, 53, 24,  −8, 2} ⅜ { 3, −11, 50,29,  −9, 2} 7/16 { 3, −11, 44, 35, −10, 3} ½ { 3, −10, 35, 44, −11, 3}

In the JEM, BIO is applied to all bi-predicted blocks when the twopredictions are from different reference pictures. When LIC is enabledfor a CU, BIO is disabled.

In the JEM, OBMC is applied for a block after normal MC process. Toreduce the computational complexity, BIO is not applied during the OBMCprocess. This means that BIO is only applied in the MC process for ablock when using its own MV and is not applied in the MC process whenthe MV of a neighboring block is used during the OBMC process.

2.2.19. Decoder-Side Motion Vector Refinement

In bi-prediction operation, for the prediction of one block region, twoprediction blocks, formed using a motion vector (MV) of list0 and a MVof list1, respectively, are combined to form a single prediction signal.In the decoder-side motion vector refinement (DMVR) method, the twomotion vectors of the bi-prediction are further refined by a bilateraltemplate matching process. The bilateral template matching applied inthe decoder to perform a distortion-based search between a bilateraltemplate and the reconstruction samples in the reference pictures inorder to obtain a refined MV without transmission of additional motioninformation.

In DMVR, a bilateral template is generated as the weighted combination(i.e., average) of the two prediction blocks, from the initial MV0 oflist0 and MV1 of list1, respectively, as shown in FIG. 34 . The templatematching operation consists of calculating cost measures between thegenerated template and the sample region (around the initial predictionblock) in the reference picture. For each of the two reference pictures,the MV that yields the minimum template cost is considered as theupdated MV of that list to replace the original one. In the JEM, nine MVcandidates are searched for each list. The nine MV candidates includethe original MV and 8 surrounding MVs with one luma sample offset to theoriginal MV in either the horizontal or vertical direction, or both.Finally, the two new MVs, i.e., MV0′ and MV1′, as shown in FIG. 33 , areused for generating the final bi-prediction results. A sum of absolutedifferences (SAD) is used as the cost measure. Please note that whencalculating the cost of a prediction block generated by one surroundingMV, the rounded MV (to integer pel) is actually used to obtain theprediction block instead of the real MV.

DMVR is applied for the merge mode of bi-prediction with one MV from areference picture in the past and another from a reference picture inthe future, without the transmission of additional syntax elements. Inthe JEM, when LIC, affine motion, FRUC, or sub-CU merge candidate isenabled for a CU, DMVR is not applied.

3. Related Tools 3.1.1. Diffusion Filter

In JVET-L0157, diffusion filter is proposed, wherein the intra/interprediction signal of the CU may be further modified by diffusionfilters.

3.1.1.1. Uniform Diffusion Filter

The Uniform Diffusion Filter is realized by convolving the predictionsignal with a fixed mask that is either given as h^(I) or as h^(IV),defined below. Besides the prediction signal itself, one line ofreconstructed samples left and above of the block are used as an inputfor the filtered signal, where the use of these reconstructed samplescan be avoided on inter blocks.

Let pred be the prediction signal on a given block obtained by intra ormotion compensated prediction. In order to handle boundary points forthe filters, the prediction signal needs to be extended to a predictionsignal pred_(ext). This extended prediction can be formed in two ways:Either, as an intermediate step, one line of reconstructed samples leftand above the block are added to the prediction signal and then theresulting signal is mirrored in all directions. Or only the predictionsignal itself is mirrored in all directions. The latter extension isused for inter blocks. In this case, only the prediction signal itselfcomprises the input for the extended prediction signal pred_(ext).

If the filter h^(I) is to be used, it is proposed to replace theprediction signal pred by:

h ^(I)*pred,

using the aforementioned boundary extension. Here, the filter mask h^(I)is given as:

$\begin{matrix}{h^{I} = {(0.25)^{4}\begin{pmatrix}0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 4 & 0 & 4 & 0 & 0 & 0 \\0 & 0 & 6 & 0 & 16 & 0 & 6 & 0 & 0 \\0 & 4 & 0 & 24 & 0 & 24 & 0 & 4 & 0 \\1 & 0 & 16 & 0 & 36 & 0 & 16 & 0 & 1 \\0 & 4 & 0 & 24 & 0 & 24 & 0 & 4 & 0 \\0 & 0 & 6 & 0 & 16 & 0 & 6 & 0 & 0 \\0 & 0 & 0 & 4 & 0 & 4 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0\end{pmatrix}}} & {{Eq}.(49)}\end{matrix}$

If the filter h^(IV) is to be used, it is proposed to replace theprediction signal pred by:

h ^(IV)*pred.  Eq. (50)

Here, the filter h^(IV) is given as:

h ^(IV) =h ^(I) *h ^(I) *h ^(I) *h ^(I)  Eq. (51)

3.1.1.2. Directional Diffusion Filter

Instead of using signal adaptive diffusion filters, directional filters,a horizontal filter h^(hor) and a vertical filter h^(ver), are usedwhich still have a fixed mask. More precisely, the uniform diffusionfiltering corresponding to the mask h^(I) of the previous section issimply restricted to be either applied only along the vertical or alongthe horizontal direction. The vertical filter is realized by applyingthe fixed filter mask:

$\begin{matrix}{h_{ver} = {(0.5)^{4}\begin{pmatrix}1 \\0 \\4 \\0 \\6 \\0 \\4 \\0 \\1\end{pmatrix}}} & {{Eq}.(52)}\end{matrix}$

to the prediction signal and the horizontal filter is realized by usingthe transposed mask:

h _(hor) =h _(ver) ^(t)  Eq. (53)

3.1.2. Bilateral Filter

Bilateral filter is proposed in JVET-L0406, and it is always applied toluma blocks with non-zero transform coefficients and slice quantizationparameter larger than 17. Therefore, there is no need to signal theusage of the bilateral filter. Bilateral filter, if applied, isperformed on decoded samples right after the inverse transform. Inaddition, the filter parameters, i.e., weights are explicitly derivedfrom the coded information.

The filtering process is defined as:

P′ _((0,0)) =P _(0,0)+Σ_(k=1) ^(K) W _(k)(abs(P _(k,0) −P _(0,0)))×(P_(k,0) −P _(0,0)),  Eq. (54)

where P_(0,0) is the intensity of the current sample and P′_(0,0) is themodified intensity of the current sample, P_(k,0) and W_(k) are theintensity and weighting parameter for the k-th neighboring sample,respectively. An example of one current sample and its four neighboringsamples (i.e., K=4) is depicted in FIG. 35 .

More specifically, the weight W_(k) (x) associated with the k-thneighboring sample is defined as follows:

$\begin{matrix}{{W_{k}(x)} = {{Distance}_{k} \times {{Range}_{k}(x)}{wherein}}} & {{Eq}.(55)}\end{matrix}$ $\begin{matrix}{{{Distance}_{k} = {{e^{({- \frac{10000}{2\sigma_{d}^{2}}})}/1} + {4*e^{({- \frac{10000}{2\sigma_{d}^{2}}})}}}},} & {{Eq}.(56)}\end{matrix}$${{Range}_{k}(x)} = e^{({- \frac{x^{2}}{8*{({{QP} - 17})}*{({{QP} - 17})}}})}$

and σ_(d) is dependent on the coded mode and coding block sizes. Thedescribed filtering process is applied to intra-coded blocks, andinter-coded blocks when TU is further split, to enable parallelprocessing.

To better capture statistical properties of video signal, and improveperformance of the filter, weights function resulted from Eq. (55) arebeing adjusted by the ad parameter, tabulated in Table as beingdependent on coding mode and parameters of block partitioning (minimalsize).

TABLE 11 Value of σ_(d) for different block sizes and coding modesMin(block width, block height) Intra mode Inter mode 4 82 62 8 72 52Other 52 32

To further improve the coding performance, for inter-coded blocks whenTU is not split, the intensity difference between current sample and oneof its neighboring samples is replaced by a representative intensitydifference between two windows covering current sample and theneighboring sample. Therefore, the equation of filtering process isrevised to:

$\begin{matrix}{P_{0,0}^{\prime} = {P_{0,0} + {\sum_{k = 1}^{N}{{W_{k}( {\frac{1}{M}{\sum_{m = {{- M}/2}}^{M/2}{{abs}( {P_{k,m} - P_{0,m}} )}}} )} \times ( {P_{k,0} - P_{0,0}} )}}}} & {{Eq}.(57)}\end{matrix}$

wherein P_(k, m) and P_(0, m) represent the m-th sample value within thewindows centered at P_(k, 0) and P_(0, 0), respectively. In thisproposal, the window size is set to 3×3. An example of two windowscovering P_(2, 0) and P_(0, 0) are depicted in FIG. 36 .

3.1.3. Intra Block Copy Decoder Aspect:

In some aspects, the current (partially) decoded picture is consideredas a reference picture. This current picture is put in the last positionof reference picture list 0. Therefore, for a slice using the currentpicture as the only reference picture, its slice type is considered as aP slice. The bitstream syntax in this approach follows the same syntaxstructure for inter coding while the decoding process is unified withinter coding. The only outstanding difference is that the block vector(which is the motion vector pointing to the current picture) always usesinteger-pel resolution.

Changes from block level CPR_flag approach are:

-   -   In encoder search for this mode, both block width and height are        smaller than or equal to 16.    -   Enable chroma interpolation when luma block vector is an odd        integer number.    -   Enable adaptive motion vector resolution (AMVR) for CPR mode        when the SPS flag is on. In this case, when AMVR is used, a        block vector can switch between 1-pel integer and 4-pel integer        resolutions at block level.

Encoder Aspect:

The encoder performs RD check for blocks with either width or height nolarger than 16. For non-merge mode, the block vector search is performedusing hash-based search first. If there is no valid candidate found fromhash search, block matching based local search will be performed.

In the hash-based search, hash key matching (32-bit cyclic redundancycheck (CRC)) between the current block and a reference block is extendedto all allowed block sizes. The hash key calculation for every positionin current picture is based on 4×4 blocks. For the current block of alarger size, a hash key matching to a reference block happens when allits 4×4 blocks match the hash keys in the corresponding referencelocations. If multiple reference blocks are found to match the currentblock with the same hash key, the block vector costs of each candidatesare calculated and the one with minimum cost is selected.

In block matching search, the search range is set to be 64 pixels to theleft and on top of current block.

3.1.4. History Based Motion Vector Prediction

A history-based MVP (HMVP) method is proposed wherein a HMVP candidateis defined as the motion information of a previously coded block. Atable with multiple HMVP candidates is maintained during theencoding/decoding process. The table is emptied when a new slice isencountered. Whenever there is an inter-coded block, the associatedmotion information is added to the last entry of the table as a new HMVPcandidate. The overall coding flow is depicted in FIG. 37 . In oneexample, the table size is set to be L (e.g., L=16 or 6, or 44), whichindicates up to L HMVP candidates may be added to the table.

-   1) In one embodiment, if there are more than L HMVP candidates from    the previously coded blocks, a First-In-First-Out (FIFO) rule is    applied so that the table always contains the latest previously    coded L motion candidates. FIG. 38 depicts an example wherein the    FIFO rule is applied to remove a HMVP candidate and add a new one to    the table used in the proposed method.-   2) In another embodiment, whenever adding a new motion candidate    (such as the current block is inter-coded and non-affine mode), a    redundancy checking process is applied firstly to identify whether    there are identical or similar motion candidates in lookup tables    (LUTs).

3.2. JVET-M0101 3.2.1. Adding HEVC-Style Weighted Prediction

The following table show an example of syntax element. In order toimplement the HEVC-style weighted prediction, the following syntaxchanges as shown in bold text can be made to PPS and slice header:

TABLE 12 Example of syntax element pic_parameter_set_rbsp( ) {Descriptor  pps_pic_parameter_set_id ue(v)  pps_seq_parameter_set_idue(v)  init_qp_minus26 se(v)  transform_skip_enabled_flag u(1) cu_qp_delta_enabled_flag u(1)  if( cu_qp_delta_enabled_flag )  diff_cu_qp_delta_depth ue(v)  pps_cb_qp_offset se(v)  pps_cr_qp_offsetse(v)  pps_slice_chroma_qp_offsets_present_flag u(1)  weighted_pred_flagu(1)  weighted_bipred_flag u(1)  deblocking_filter_control_present_flagu(1)  if( deblocking_filter_control_present_flag ) {  deblocking_filter_override_enabled_flag u(1)  pps_deblocking_filter_disabled_flag u(1)   if(!pps_deblocking_filter_disabled_flag ) {    pps_beta_offset_div2 se(v)   pps_tc_offset_div2 se(v)   }  }  rbsp_trailing_bits( ) }

slice_header( ) { Descriptor  slice_pic_parameter_set_id ue(v) slice_address u(v)  slice_type ue(v)  if(partition_constraints_override_enabled_flag ) {  partition_constraints_override_flag ue(v)   if(partition_constraints_override_flag ) {   slice_log2_diff_min_qt_min_cb_luma ue(v)   slice_max_mtt_hierarchy_depth_luma ue(v)    if(slice_max_mtt_hierarchy_depth_luma != 0 )    slice_log2_diff_max_bt_min_qt_luma ue(v)    slice_log2_diff_max_tt_min_qt_luma ue(v)    }    if( slice_type = =I && qtbtt_dual_tree_intra_flag ) {    slice_log2_diff_min_qt_min_cb_chroma ue(v)    slice_max_mtt_hierarchy_depth_chroma ue(v)     if(slice_max_mtt_hierarchy_depth_chroma != 0 )     slice_log2_diff_max_bt_min_qt_chroma ue(v)     slice_log2_diff_max_tt_min_qt_chroma ue(v)     }    }   }  }  if (slice_type != I ) {   if( sps_temporal_mvp_enabled_flag )   slice_temporal_mvp_enabled_flag u(1)   if( slice_type = = B )   mvd_l1_zero_flag u(1)   if( slice_temporal_mvp_enabled_flag ) {   if( slice_type = = B )     collocated_from_10_flag u(1)   }    if(( weighted_pred_flag && slice_type = = P ) | |    ( weighted_bipred_flag && slice_type = = B ) )    pred_weight_table( )   six_minus_max_num_merge_cand ue(v)   if(sps_affine_enable_flag )    five_minus_max_num_subblock_merge_cand ue(v) }  slice_qp_delta se(v)  if( pps_slice_chroma_qp_offsets_present_flag ){   slice_cb_qp_offset se(v)   slice_cr_qp_offset se(v)  }  if(sps_sao_enabled_flag ) {   slice_sao_luma_flag u(1)   if( ChromaArrayType != 0 )    slice_sao_chroma_flag u(1)  }  if(sps_alf_enabled_flag ) {   slice_alf_enabled_flag u(1)   if(slice_alf_enabled_flag )    alf_data( )  }  dep_quant_enabled_flag u(1) if( !dep_quant_enabled_flag )   sign_data_hiding_enabled_flag u(1)  if(deblocking_filter_override_enabled_flag )  deblocking_filter_override_flag u(1)  if(deblocking_filter_override_flag ) {  slice_deblocking_filter_disabled_flag u(1)   if(!slice_deblocking_filter_disabled_flag ) {   slice_beta_offset_div2se(v)   slice_tc_offset_div2 se(v)   }  }  byte_alignment( ) }

pred_weight_table( ) { Descriptor  luma_log2_weight_denom ue(v) if( ChromaArrayType != 0 )   delta_chroma_log2_weight_denom se(v) for( i = 0; i <= num_ref_idx_l0_active_minus1; i++ )  luma_weight_l0_flag[ i ] u(1)  if( ChromaArrayType != 0 )   for( i =0; i <= num_ref_idx_l0_active_minus1; i++ )   chroma_weight_l0_flag[ i ] u(1)  for( i = 0; i <=num_ref_idx_l0_active_minus1; i++ ) {   if( luma_weight_l0_flag[ i ] ) {   delta_luma_weight_l0[ i ] se(v)    luma_offset_l0[ i ] se(v)   }  if( chroma_weight_l0_flag[ i ] )    for( j=0; j < 2; j++ ) {    delta_chroma_weight_l0[ i ] [ j ] se(v)    delta_chroma_offset_l0[ i ] [ j ] se(v)    }  }  if( slice_type = =B ) {   for( i = 0; i <= num_ref_idx_l1_active_minus1; i++ )   luma_weight_l1_flag[ i ] u(1)   if( ChromaArrayType != 0 )    for( i=0; i <= num_ref_idx_l1_active_minus1; i++ )    chroma_weight_l1_flag[ i ] u(1)   for( i= 0; i <=num_ref_idx_l1_active_minus1; i++ ) {   if( luma_weight_l1_flag[ i ] ) {     delta_luma_weight_l1[ i ] se(v)    luma_offset_l1[ i ] se(v)    }    if( chroma_weight_l1_flag[ i ] )    for( j = 0; j < 2; j++ ){      delta_chroma_weight_l1[ i ] [ j ]se(v)      delta_chroma_offset_l1[ i ] [ j ] se(v)     }   }  } }3.2.2. Invoking (Bi-Prediction with Weighted Averaging (BWA), a.k.a.,GBI) and Weighted Prediction (WP) in a Mutually Exclusive Manner

Though BWA and WP both apply weights to the motion compensatedprediction signals, the specific operations are different. In thebi-prediction case, WP applies a linear weight and a constant offset toeach of the prediction signals depending on the (weight, offset)parameters associated with the ref_idx that is used to generate theprediction signal. Whereas there are some range constraints on these(weight, offset) values, the allowed ranges are relatively large andthere is no normalization constraint on the parameter values. WPparameters are signaled at the picture level (in slice headers). WP hasbeen shown to provide very large coding gain for fading sequences, andis generally expected to be enabled for such content.

BWA uses a CU level index to indicate how to combine the two predictionsignals in the case of bi-prediction. The BWA applies weightedaveraging, i.e., the two weights add up to 1. BWA provides about 0.66%coding gain for the common test conditions (CTC) random access (RA)configuration, but is much less effective than WP for the fading content(JVET-L0201).

Method #1:

The PPS syntax element weight_bipred_flag is checked to determine if thegbi_idx is signaled at the current CU. The syntax signaling is modifiedas follows in bold text:

TABLE 13 Example of syntax element coding_unit( x0, y0, cbWidth,cbHeight, treeType ) { Descriptor ...  if( sps_gbi_enabled_flag &&inter_pred_idc[ x0 ][ y0 ] = = PRED_BI &&    !weighted_bipred_flag &&cbWidth * cbHeight >= 256 )   gbi_idx[ x0 ][ y0 ] ae(v) ... }

The first alternative will disable BWA for all the reference pictures ofthe current slice, if the current slice refers to a PPS for whichweighted_bipred_flag is set to 1.

Method #2:

BWA is disabled only if both of the reference pictures used in thebi-prediction have turned on weighted prediction, i.e., the (weight,offset) parameters of these reference pictures have non-default values.This allows the bi-predicted CUs that use reference pictures withdefault WP parameters (i.e., WP is not invoked for these CUs) to stillbe able to use BWA. The syntax signaling is modified as follows in boldtext:

TABLE 14 Example of syntax element coding_unit( x0, y0, cbWidth,cbHeight, treeType ) { Descriptor ...  if( sps_gbi_enabled_flag &&inter_pred_idc[ x0 ][ y0 ] = = PRED_BI &&    luma_weight_10_flag[ ref_idx_l0[ x0 ] [ y0 ] ] == 0 &&    chroma_weight_10_flag[ ref_idx_l0[ x0 ] [ y0 ] ] == 0 &&    luma_weight_l1_flag[ ref_idx_l1[ x0 ] [ y0 ] ] == 0 &&  chroma_weight_l1_flag[ ref_idx_l1[ x0 ] [ y0 ] ] == 0 &&    cbWidth * cbHeight >= 256 )   gbi_idx[ x0 ][ y0 ] ae(v) ... }

4. Problems

In LIC, two parameters including scaling parameter a and offset b needto be derived by using neighboring reconstructed pixels, which may causelatency issue.

Hybrid intra and inter prediction, diffusion filter, bilateral filter,OBMC and LIC need to further modify the inter prediction signal indifferent ways, and they all have latency issue.

5. Some Example Embodiments and Techniques

-   -   1. Examples below are provided to explain general concepts.        These examples should not be interpreted in a narrow way.        Furthermore, the examples below can be combined in any manner.        It is proposed that LIC could only be performed for blocks        located at CTU boundaries (called boundary blocks), and        neighboring reconstructed samples out of the current CTU may be        used for deriving LIC parameters. In this case, for those blocks        that are not located CTU boundaries (called inner blocks), LIC        is always disabled without being signaled.        -   a. Selection of neighboring reconstructed samples outside            current CTU may depend on the position of the block relative            to the CTU covering the current block.        -   b. In one example, for blocks at the left boundary of a CTU,            only left reconstructed neighboring samples of the CU may be            used to derive the LIC parameters.        -   c. In one example, for blocks at the top boundary of a CTU,            only above reconstructed neighboring samples of the block            may be used to derive the LIC parameters.        -   d. In one example, for blocks at the top-left corner of a            CTU, left and/or above reconstructed neighboring samples of            the block may be used to derive the LIC parameters.        -   e. In one example, for blocks at the top-right corner of a            CTU, top-right and/or above reconstructed neighboring            samples of the block are used to derive the LIC parameters.        -   f. In one example, for blocks at the bottom-left corner of a            CTU, bottom-left and/or left reconstructed neighboring            samples of the block are used to derive the LIC parameters.    -   2. It is proposed that sets of LIC parameters may be derived for        blocks located at CTU boundary only, and inner blocks of the CTU        may inherit from one or multiple sets of these LIC parameter        sets.        -   a. In one example, a LIC parameter lookup table is            maintained for each CTU, and each set of the derived LIC            parameter is inserted into the LIC parameter table. Some            method can be used to maintain the LIC parameter lookup            table.        -   b. Alternatively, such lookup table is maintained for each            reference picture, and when deriving the LIC parameters, LIC            parameters are derived for all reference pictures.        -   c. In one example, such lookup table is emptied at the            beginning of each CTU or CTU row or slice or tile or tile            group or picture.        -   d. In one example, for inner block coded with AMVP mode or            affine inter mode, if LIC flag is true, the used set of LIC            parameters is explicitly signaled. For example, an index is            signaled to indicate which entry of the lookup table is used            for each reference picture.            -   i. In one example, for uni-predicted block, if there is                no valid entry in the lookup table for the reference                picture, the LIC flag shall be false.            -   ii. In one example, for bi-predicted block, if there is                no valid entry in the lookup table for any of the                reference picture, the LIC flag shall be false.            -   iii. In one example, for bi-predicted block, if there is                valid entry in the lookup table for at least one of the                reference pictures, the LIC flag can be true. One LIC                parameter index is signaled for each reference picture                with valid LIC parameters.        -   e. In one example, more than one lookup tables are            maintained.            -   i. In one example, when encoding/decoding the current                CTU, it only uses parameters from lookup tables                generated by some previously encoded/decoded CTUs, and                the lookup table generated by the current CTU is used                for some following CTUs.            -   ii. In one example, each lookup table may correspond to                one reference picture/one reference picture list/a                certain range of block sizes/a certain coded mode/a                certain block shape, etc. al.        -   f. In one example, if an inner block is coded with merge or            affine merge mode, for spatial or/and temporal merge            candidate, both LIC flag and LIC parameters are inherited            from the corresponding neighboring block.            -   i. Alternatively, the LIC flag is inherited and the LIC                parameter may be signaled explicitly.            -   ii. Alternatively, the LIC flag is signaled explicitly                and the LIC parameter may be inherited.            -   iii. Alternatively, both LIC flag and LIC parameter are                signaled explicitly.            -   iv. Alternatively, the differences between the LIP                parameters of the block and the inherited parameters are                signaled.        -   g. In one example, for boundary block coded with AMVP mode            or affine inter mode, if LIC flag is true, the used LIC            parameter is derived implicitly using same methods as in            2.2.7.        -   h. In one example, if a boundary block is coded with merge            or affine merge mode, for spatial or/and temporal merge            candidate, both LIC flag and LIC parameter are inherited            from the corresponding neighboring block.            -   i. Alternatively, the LIC flag is inherited and the LIC                parameters may be signaled explicitly.            -   ii. Alternatively, the LIC flag is signaled explicitly                and the LIC parameters may be inherited.            -   iii. Alternatively, both LIC flag and LIC parameter are                signaled explicitly.        -   i. In one example, if a block is coded with merge mode, for            combined merge candidate or average merge candidate, LIC is            always disabled.            -   i. Alternatively, if LIC flag of any of the two merge                candidates that are used for generating the combined                merge candidate or average merge candidate is true, the                LIC flag is set to true.            -   ii. For an inner block, if both merge candidates that                are used for generating the combined merge candidate or                average merge candidate use LIC, it may inherit LIC                parameters from any of them.            -   iii. Alternatively, the LIC flag is inherited and the                LIC parameter may be signaled explicitly.            -   iv. Alternatively, the LIC flag is signaled explicitly                and the LIC parameter may be inherited.            -   v. Alternatively, both LIC flag and LIC parameter are                signaled explicitly.        -   j. In one example, if a block is coded with merge mode from            a HMVP merge candidate, LIC is always disabled.            -   i. Alternatively, if a block is coded with merge mode                from a HMVP merge candidate, LIC is always enabled.            -   ii. Alternatively, if LIC flag of the HMVP merge                candidate is true, the LIC flag is set to be true.                -   1. LIC flag is signaled explicitly.            -   iii. Alternatively, if LIC flag of the HMVP merge                candidate is true, the LIC flag is set to be true, and                the LIP parameters are inherited from the HMVP merge                candidate.                -   1. Alternatively, LIC parameters are signaled                    explicitly.                -   2. Alternatively, LIC parameters are derived                    implicitly.    -   3. It is proposed that hybrid intra and inter prediction (also        known as combined intra-inter prediction, CIIP for short),        diffusion filter, bilateral filter, transform domain filtering        method, OBMC, LIC or any other tools that modify the inter        prediction signal or modify the reconstructed block from motion        compensation (i.e., causing latency issues) are exclusively        used.        -   a. In one example, if LIC is enabled, all other tools are            disabled implicitly. If LIC flag is true (either explicitly            signaled or implicitly derived), on/off flag of other tools            (if there is any) are not signaled and implicitly derived to            be off.        -   b. In one example, if hybrid intra and inter prediction is            enabled, all other tools are disabled implicitly. If hybrid            intra and inter prediction flag is true (either explicitly            signaled or implicitly derived), on/off flag of other tools            (if there is any) are not signaled and implicitly derived to            be off.        -   c. In one example, if diffusion filter is enabled, all other            tools are disabled implicitly. If diffusion filter flag is            true (either explicitly signaled or implicitly derived),            on/off flag of other tools (if there is any) are not            signaled and implicitly derived to be off.        -   d. In one example, if OBMC is enabled, all other tools are            disabled implicitly. If OBMC flag is true (either explicitly            signaled or implicitly derived), on/off flag of other tools            (if there is any) are not signaled and implicitly derived to            be off.        -   e. In one example, if bilateral filter is enabled, all other            tools are disabled implicitly. If bilateral filter flag is            true (either explicitly signaled or implicitly derived),            on/off flag of other tools (if there is any) are not            signaled and implicitly derived to be off.        -   f. Different tools may be checked in order. Alternatively,            furthermore, such checking process terminates when one of            the above tools is decided to be enabled.            -   i. In one example, the checking order is LIC 4 diffusion                filter 4 hybrid intra and inter prediction 4 OBMC 4                bilateral filter.            -   ii. In one example, the checking order is LIC 4                diffusion filter 4 bilateral filter 4 hybrid intra and                inter prediction 4 OBMC.            -   iii. In one example, the checking order is LIC 4 OBMC 4                diffusion filter 4 bilateral filter 4 hybrid intra and                inter prediction.            -   iv. In one example, the checking order is LIC 4 OBMC 4                diffusion filter 4 hybrid intra and inter prediction 4                bilateral filter.            -   v. The order may be adaptively changed based on                previously coded information and/or based on coded                information of current block (e.g., block size/reference                picture/MV information/Low delay check                flag/tile/picture/slice types), such as based on the                modes of neighboring blocks.        -   g. For any one of the above mentioned tools (e.g., CIIP,            LIC, diffusion filter, bilateral filter, transform domain            filtering method), whether to automatically disable it            and/or use different ways for decoding the current block may            depend on the coded modes of the neighboring or non-adjacent            row or columns.            -   i. Alternatively, for any one of the above mentioned                tools (e.g., CIIP, LIC, diffusion filter, bilateral                filter, transform domain filtering method), whether to                automatically disable it may depend on all the coded                modes of the neighboring or non-adjacent row or columns.            -   ii. Alternatively, for any one of the above mentioned                tools (e.g., CIIP, LIC, diffusion filter, bilateral                filter, transform domain filtering method), whether to                enable it may depend on at least one of the samples in                the neighboring or non-adjacent row or columns is NOT                coded with certain modes.            -   iii. In one example, the neighboring or non-adjacent row                may include the above row and/or above-right row,            -   iv. In one example, the neighboring or non-adjacent                column may include the left column and/or below-left                column.            -   v. In one example, the coded modes/certain modes may                include intra mode and/or combined intra-inter mode                (CIIP).            -   vi. In one example, if any one neighboring/non-adjacent                block in the neighboring or non-adjacent row or columns                is coded with intra and/or CIIP, such method is                disabled.            -   vii. In one example, if all of neighboring/non-adjacent                blocks in the neighboring or non-adjacent row or columns                is coded with intra and/or CIIP, such method is                disabled.            -   viii. In one example, different methods may include                short-tap filters/fewer neighboring samples to be                utilized for LIC parameter derivation, padding of                reference samples etc. al.        -   h. For any one of the above mentioned tools (e.g., CIIP,            LIC, diffusion filter, bilateral filter, transform domain            filtering method), it is disabled when there is at least one            above neighboring/non-adjacent above neighboring block in            the neighboring or non-adjacent row is intra coded and/or            combined intra-inter mode coded.        -   i. For any one of the above mentioned tools (e.g., CIIP,            LIC, diffusion filter, bilateral filter, transform domain            filtering method), it is disabled when there is at least one            left neighboring/non-adjacent left neighboring block in the            neighboring or non-adjacent column is intra coded and/or            combined intra-inter mode coded.        -   j. For any one of the above mentioned tools (e.g., CIIP,            LIC, diffusion filter, bilateral filter, transform domain            filtering method), it is disabled when all blocks in the            neighboring or non-adjacent row/column is intra coded and/or            combined intra-inter mode coded.        -   k. In one example, for LIC coded blocks, the neighboring            samples coded with intra mode and/or hybrid intra and inter            mode are excluded from derivation of LIC parameters.        -   l. In one example, for LIC coded blocks, the neighboring            samples coded with non-intra mode and/or non-CIIP mode may            be included from derivation of LIC parameters.    -   4. When certain tool is disabled for one block (such as when all        neighboring samples are intra coded), such a coding tool may        still be applied but in a different way.        -   a. In one example, short-tap filters may be applied.        -   b. In one example, padding of reference samples may be            applied.        -   c. In one example, neighboring row/column and/or            non-adjacent row/column of blocks in reference pictures (via            motion compensation if needed) may be utilized as a            replacement of current blocks' neighboring row/column and/or            non-adjacent row/column.    -   5. It is proposed that LIC is used exclusively with combined        inter-intra prediction (CIIP). In some implementations, LIC and        combined inter-intra prediction (CIIP) are exclusive of each        other.        -   a. In one example, CIIP information may be signaled after            LIC information.            -   i. In one example, whether to signal CIIP information                may depend on the signaled/inferred LIC information.            -   ii. Alternatively, furthermore, whether to signal CIIP                information may depend on both LIC information and                weighted prediction information associated with at least                one reference picture of current block or of current                tile/tile group/picture containing current block.            -   iii. The information may be signaled in sequence                parameter set (SPS)/picture parameter set (PPS)/slice                header/tile group header/tile/CTU/CU        -   b. Alternatively, LIC information may be signaled after CIIP            information.            -   i. In one example, whether to signal LIC information may                depend on the signaled/inferred CIIP information.            -   ii. Alternatively, furthermore, whether to signal LIC                information may depend on both CIIP information and                weighted prediction information associated with at least                one reference picture of current block or of current                tile/tile group/picture containing current block.            -   iii. The information may be signaled in SPS/PPS/slice                header/tile group header/tile/CTU/CU        -   c. In one example, if LIC flag is true, syntax elements            required by CIIP are not signaled.        -   d. In one example, if CIIP flag is true, syntax elements            required by LIC are not signaled.        -   e. In one example, if CIIP is enabled, syntax elements            required by LIC are not signaled.    -   6. It is proposed that in pairwise prediction or combined-bi        prediction or other kinds of virtual/artificial candidates        (e.g., zero motion vector candidates), LIC or/and GBI or/and        weighted prediction may be disabled.        -   a. Alternatively, if one of the two candidates involved in            pairwise prediction or combined-bi prediction adopt LIC            prediction and none of the two candidates adopt weighted            prediction or GBI, LIC may be enabled for the pairwise or            combined-bi merge candidate.        -   b. Alternatively, if both candidates involved in pairwise            prediction or combined-bi prediction adopt LIC prediction,            LIC may be enabled for the pairwise or combined-bi merge            candidate.        -   c. Alternatively, if one of the two candidates involved in            pairwise prediction or combined-bi prediction adopt weighted            prediction and none of the two candidates adopt LIC            prediction or GBI, weighted prediction may be enabled for            the pairwise or combined-bi merge candidate.        -   d. Alternatively, if both candidates involved in pairwise            prediction or combined-bi prediction adopt weighted            prediction, weighted prediction may be enabled for the            pairwise or combined-bi merge candidate.        -   e. Alternatively, if one of the two candidates involved in            pairwise prediction or combined-bi prediction adopt GBI and            none of the two candidates adopt LIC prediction or weighted            prediction, GBI may be enabled for the pairwise or            combined-bi merge candidate.        -   f. Alternatively, if both candidates involved in pairwise            prediction or combined-bi prediction adopt GBI and GBI index            are the same for the two candidates, GBI may be enabled for            the pairwise or combined-bi merge candidate.    -   7. It is proposed that LIC prediction or/and weighted prediction        or/and GBI may be considered in deblocking filter.        -   a. In one example, even two blocks nearby the boundary have            same motion but with different LIC parameters/weighted            prediction parameters/GBI indices, deblocking filtering            process may be applied.        -   b. In one example, if two blocks (nearby the boundary) have            different GBI index, a stronger boundary filtering strength            may be assigned.        -   c. In one example, if two blocks have different LIC flag, a            stronger boundary filtering strength may be assigned.        -   d. In one example, if two blocks adopt different LIC            parameters, a stronger boundary filtering strength may be            assigned.        -   e. In one example, if one block adopts weighted prediction            and the other block does not adopt weighted prediction, or            two blocks adopt different weighting factor (e.g., predicted            from reference pictures with different weighting factor), a            stronger boundary filtering strength may be assigned.        -   f. In one example, if two blocks nearby the boundary, one is            coded with LIC mode and the other not, deblocking filtering            may be applied even the motion vectors are same.        -   g. In one example, if two blocks nearby the boundary, one is            coded with weighted prediction mode and the other not,            deblocking filtering may be applied even the motion vectors            are same.        -   h. In one example, if two blocks nearby the boundary, one is            coded with GBI enabled (e.g., unequal weights) and the other            not, deblocking filtering may be applied even the motion            vectors are same.    -   8. It is proposed that affine mode/affine parameters/affine type        may be considered in deblocking filter.        -   a. Whether to and/or how to apply deblocking filter may            depend on the affine mode/affine parameters.        -   b. In one example, if two blocks (nearby the boundary) have            different affine mode, a stronger boundary filtering            strength may be assigned.        -   c. In one example, if two blocks (nearby the boundary) have            different affine parameters, a stronger boundary filtering            strength may be assigned.        -   d. In one example, if two blocks nearby the boundary, one is            coded with affine mode and the other not, deblocking            filtering may be applied even the motion vectors are same.    -   9. For above bullets, they may be also applicable to other kinds        of filtering process,    -   10. When LIC is conducted, the block should be divided into        VPDUs (such as 64*64 or 32*32 or 16*16) process-blocks, each        block conducts LIC procedure sequentially (that means the LIC        procedure of one process-block may depend on the LIC procedure        of another process-block), or parallelly (that means the LIC        procedure of one process-block cannot depend on the LIC        procedure of another process-block).    -   11. Alternatively, it is proposed that LIC may be used together        with multi-hypothesis prediction (as described in 2.2.13,        2.2.14, 2.2.15).        -   a. In one example, LIC flag is explicitly signaled for            multi-hypothesis AMVP and merge mode (e.g., as described in            2.2.14).            -   i. In one example, the explicitly signaled LIC flag is                applied to both AMVP mode and merge mode.            -   ii. In one example, the explicitly signaled LIC flag is                applied only to AMVP mode, while the LIC flag for the                merge mode is inherited from the corresponding merge                candidate. Different LIC flag may be used for AMVP mode                and merge mode. Meanwhile, different LIC parameters may                be derived/inherited for AMVP mode and merge mode.                -   1. Alternatively, LIC is always disabled for the                    merge mode.            -   iii. Alternatively, LIC flag is not signaled and LIC is                always disabled for AMVP mode. However, for merge mode,                LIC flag or/and LIC parameter may be inherited or                derived.        -   b. In one example, LIC flag is inherited from the            corresponding merge candidates for multi-hypothesis merge            mode (e.g., as described in 2.2.15).            -   i. In one example, LIC flag is inherited for each of the                two selected merge candidates, therefore, different LIC                flag may be inherited for the two selected merge                candidates. Meanwhile, different LIC parameter may be                derived/inherited for the two selected merge candidates.            -   ii. In one example, LIC flag is only inherited for the                1st selected merge candidate and LIC is always disabled                for the 2^(nd) selected merge candidate.        -   c. In one example, LIC flag is explicitly signaled for            multi-hypothesis inter prediction mode (e.g., as described            in 2.2.13).            -   i. In one example, if the block is predicted with merge                mode (or UMVE mode) and additional motion information,                the explicitly signaled LIC flag may be applied to both                merge mode (or UMVE mode) and the additional motion                information.            -   ii. In one example, if the block is predicted with merge                mode (or UMVE mode) and additional motion information,                the explicitly signaled LIC flag may be applied to the                additional motion information. While for merge mode, LIC                flag or/and LIC parameter may be inherited or derived.                -   1. Alternatively, LIC is always disabled for the                    merge mode.            -   iii. In one example, if the block is predicted with                merge mode (or UMVE mode) and additional motion                information, LIC flag is not signaled and disabled for                the additional motion information. While for merge mode,                LIC flag or/and LIC parameter may be inherited or                derived.            -   iv. In one example, if the block is predicted with AMVP                mode and additional motion information, the explicitly                signaled LIC flag may be applied to both AMVP mode and                the additional motion information.                -   1. Alternatively, LIC is always disabled for the                    additional motion information.            -   v. Different LIC parameters may be derived/inherited for                the merge mode (or UMVE mode)/AMVP mode and the                additional motion information.        -   d. When multi-hypothesis is applied to a block, illumination            compensation may be applied to certain prediction signals,            instead of all prediction signals.        -   e. When multi-hypothesis is applied to a block, more than            one flag may be signaled/derived to indicate the usage of            illumination compensation for prediction signals.    -   12. The above proposed methods or LIC may be applied under        certain conditions, such as block sizes, slice/picture/tile        types, or motion information.        -   a. In one example, when a block size contains smaller than            M*H samples, e.g., 16 or 32 or 64 luma samples, proposed            method or LIC are not allowed.        -   b. Alternatively, when minimum size of a block's width            or/and height is smaller than or no larger than X, proposed            method or LIC are not allowed. In one example, X is set to            8.        -   c. Alternatively, when a block's width>th1 or >=th1 and/or a            block's height>th2 or >=th2, proposed method or LIC are not            allowed. In one example, th1 and/or th2 is set to 8.        -   d. Alternatively, when a block's width<th1 or <=th1 and/or a            block's height<th2 or <a=th2, proposed method or LIC are not            allowed. In one example, th1 and/or th2 is set to 8.        -   e. In one example, LIC is disabled for affine inter modes            or/and affine merge mode.        -   f. In one example, LIC is disabled for sub-block coding            tools like ATMVP or/and STMVP or/and planar motion vector            prediction modes.        -   g. In one example, LIC is only applied to some components.            For example, LIC is applied to luma component.            -   i. Alternatively, LIC is applied to chroma component.        -   h. In one example, BIO or/and DMVR is disabled if LIC flag            is true.        -   i. In one example, LIC is disabled for bi-predicted block.        -   j. In one example, LIC is disabled for inner block coded            with AMVP mode.        -   k. In one example, LIC is only allowed for uni-predicted            block.    -   13. It is proposed that selection of neighboring samples used        for deriving LIC parameters may depend on coded information,        block shape, etc. al.        -   a. In one example, if width>=height or width>height, only            above neighboring pixels are used for deriving LIC            parameters.        -   b. In one example, if width<height, only left neighboring            pixels are used for deriving LIC parameters.    -   14. It is proposed that only one LIC flag may be signaled for a        block with geometry portioning structure (such as triangular        prediction mode). In this case, all partitions of the block (all        PUs) share the same value of LIC enabling flag.        -   a. Alternatively, for some PU, the LIC may be always            disabled regardless the signaled LIC flag.        -   b. In one example, if the block is split from the top-right            corner to the bottom-left corner, one set of LIC parameters            is derived and used for both PUs.            -   i. Alternatively, LIC is always disabled for the bottom                PU.            -   ii. Alternatively, if the top PU is coded in merge mode,                LIC flag is not signaled.        -   c. In one example, if the block is split from the top-left            corner to the bottom-right corner, LIC parameters are            derived for each PU.            -   i. In one example, above neighboring samples of the                block are used for deriving LIC parameters of the top PU                and left neighboring sample of the block are used for                deriving LIC parameters of the left PU.            -   ii. Alternatively, one set of LIC parameters is derived                and used for both PUs.        -   d. In one example, if both PUs are code in merge mode, LIC            flag is not signaled and may be inherited from merge            candidates. LIC parameters may be derived or inherited.        -   e. In one example, if one PU is coded in AMVP mode and            another PU is coded in merge mode, the signaled LIC flag may            be applied to PU coded in AMVP mode only. For PU coded in            merge mode, LIC flag or/and LIC parameters are inherited.            -   i. Alternatively, LIC flag is not signaled and is                disabled for the PU coded in AMVP mode. While, for PU                coded in merge mode, LIC flag or/and LIC parameters are                inherited.            -   ii. Alternatively, LIC is disabled for the PU coded in                merge mode.        -   f. Alternatively, if both PUs are coded in AMVP mode, one            LIC flag may be signaled for each PU.        -   g. In one example, one PU may utilize reconstructed samples            from another PU within current block which has been            reconstructed to derive LIC parameters.    -   15. It is proposed that LIC may be performed for partial pixels        instead of the whole block.        -   a. In one example, LIC may be only performed for pixels            around block boundaries only, and for other pixels within            the block, LIC is not performed.        -   b. In one example, LIC is performed for the top W×N rows or            N×H columns, wherein N is an integer number, W and H denote            the width and the height of the block. For example, N is            equal to 4.        -   c. In one example, LIC is performed for the top-left            (W-m)×(H-n) region, wherein m and n are integer numbers, W            and H denote the width and the height of the block. For            example, m and n are equal to 4.    -   16. Whether to enable or disable the above methods may be        signaled in SPS/PPS/video parameter set (VPS)/sequence        header/picture header/slice header/tile group header/group of        CTUs, etc. al.        -   a. Alternatively, which method to be used may be signaled in            SPS/PPS/VPS/sequence header/picture header/slice header/tile            group header/group of CTUs, etc.        -   b. Alternatively, whether to enable or disable the above            methods and/or which method to be applied may be dependent            on block dimension, video processing data unit (VPDU),            picture type, low delay check flag, coded information of            current block (such as reference pictures, uni or            bi-prediction) or previously coded blocks.

6. Additional Embodiments

Method #1:

The PPS syntax element weight_bipred_flag is checked to determine if theLIC_enabled_flag is signaled at the current CU. The syntax signaling ismodified as follows in bold text:

TABLE 15 Example of syntax element coding_unit( x0, y0, cbWidth,cbHeight, treeType ) { Descriptor ...  if( sps_LIC_enabled_flag && ((inter_pred_idc[ x0 ] [ y0 ] = = PRED_BI && !weighted_bipred_flag) ∥(inter_pred_idc[ x0 ] [ y0 ] = = PRED_UNI && !weighted_pred_flag)) ) {  LIC_enabled_flag [ x0 ][ y0] ae(v)   ...  } ... }

The first alternative will disable LIC for all the reference pictures ofthe current slice/tile/tile group, for example,

-   -   1. if the current slice refers to a PPS for which        weighted_bipred_flag is set to 1 and current block is        bi-predicted;    -   2. if the current slice refers to a PPS for which        weighted_pred_flag is set to 1 and current block is        uni-predicted;

Method #2:

For the bi-prediction case:

LIC is disabled only if both of the reference pictures used in thebi-prediction have turned on weighted prediction, i.e., the (weight,offset) parameters of these reference pictures have non-default values.This allows the bi-predicted CUs that use reference pictures withdefault WP parameters (i.e., WP is not invoked for these CUs) to stillbe able to use LIC. For the uni-prediction case:

LIC is disabled only if the reference picture used in the uni-predictionhave turned on weighted prediction, i.e., the (weight, offset)parameters of these reference pictures have non-default values. Thisallows the uni-predicted CUs that use reference pictures with default WPparameters (i.e., WP is not invoked for these CUs) to still be able touse LIC. The syntax is modified as follows in bold text:

TABLE 16 Example of syntax element coding_unit( x0, y0, cbWidth,cbHeight, treeType ) { Descriptor ...   if( sps_gbi_enabled_flag &&    ((inter_pred_idc[ x0 ] [ y0 ] = = PRED_BI &&      luma_weight_l0_flag[ ref_idx_l0[ x0 ] [ y0 ] ] == 0 &&      chroma_weight_l0_flag[ ref_idx_l0[ x0 ] [ y0 ] ] == 0 &&      luma_weight_l1_flag[ ref_idx_l1[ x0 ] [ y0 ] ] == 0 &&  chroma_weight_l1_flag[ ref_idx_l1[ x0 ] [ y0 ] ] == 0 ) ∥ (inter_pred_idc[ x0 ] [ y0 ] = =PRED_UNI &&      luma_weight_lX_flag [ ref_idx_lX[ x0 ] [ y0 ] ] == 0 &&     chroma_weight_IX_flag [ ref_idx_IX[ x0 ] [ y0 ] ] == 0&& ) )    )    LIC_enabled_flag [ x0 ][ y0 ] ae(v) ... }

In above table, X indicates the reference picture list (X being 0 or 1).

For above examples, the following may apply:

-   -   sps_LIC_enabled_flag which controls the usage of LIC per        sequence may be replaced by indications of usage of LIC per        picture/view/slice/tile/tile groups/CTU rows/regions/multiple        CTUs/CTU.    -   the control of signalling of LIC_enabled_flag may further depend        on block dimensions.    -   In one example, the control of signalling of LIC_enabled_flag        may further depend on gbi index.

In one example, the control of signalling of gbi index may furtherdepend on LIC_enabled_flag.

FIG. 39 is a block diagram illustrating an example of the architecturefor a computer system or other control device 2600 that can be utilizedto implement various portions of the presently disclosed technology. InFIG. 39 , the computer system 2600 includes one or more processors 2605and memory 2610 connected via an interconnect 2625. The interconnect2625 may represent any one or more separate physical buses, point topoint connections, or both, connected by appropriate bridges, adapters,or controllers. The interconnect 2625, therefore, may include, forexample, a system bus, a Peripheral Component Interconnect (PCI) bus, aHyperTransport or industry standard architecture (ISA) bus, a smallcomputer system interface (SCSI) bus, a universal serial bus (USB), IIC(I2C) bus, or an Institute of Electrical and Electronics Engineers(IEEE) standard 674 bus, sometimes referred to as “Firewire.”

The processor(s) 2605 may include central processing units (CPUs) tocontrol the overall operation of, for example, the host computer. Incertain embodiments, the processor(s) 2605 accomplish this by executingsoftware or firmware stored in memory 2610. The processor(s) 2605 maybe, or may include, one or more programmable general-purpose orspecial-purpose microprocessors, digital signal processors (DSPs),programmable controllers, application specific integrated circuits(ASICs), programmable logic devices (PLDs), or the like, or acombination of such devices.

The memory 2610 can be or include the main memory of the computersystem. The memory 2610 represents any suitable form of random accessmemory (RAM), read-only memory (ROM), flash memory, or the like, or acombination of such devices. In use, the memory 2610 may contain, amongother things, a set of machine instructions which, when executed byprocessor 2605, causes the processor 2605 to perform operations toimplement embodiments of the presently disclosed technology.

Also connected to the processor(s) 2605 through the interconnect 2625 isa (optional) network adapter 2615. The network adapter 2615 provides thecomputer system 2600 with the ability to communicate with remotedevices, such as the storage clients, and/or other storage servers, andmay be, for example, an Ethernet adapter or Fiber Channel adapter.

FIG. 40 shows a block diagram of an example embodiment of a device 2700that can be utilized to implement various portions of the presentlydisclosed technology. The mobile device 2700 can be a laptop, asmartphone, a tablet, a camcorder, or other types of devices that arecapable of processing videos. The mobile device 2700 includes aprocessor or controller 2701 to process data, and memory 2702 incommunication with the processor 2701 to store and/or buffer data. Forexample, the processor 2701 can include a central processing unit (CPU)or a microcontroller unit (MCU). In some implementations, the processor2701 can include a field-programmable gate-array (FPGA). In someimplementations, the mobile device 2700 includes or is in communicationwith a graphics processing unit (GPU), video processing unit (VPU)and/or wireless communications unit for various visual and/orcommunications data processing functions of the smartphone device. Forexample, the memory 2702 can include and store processor-executablecode, which when executed by the processor 2701, configures the mobiledevice 2700 to perform various operations, e.g., such as receivinginformation, commands, and/or data, processing information and data, andtransmitting or providing processed information/data to another device,such as an actuator or external display. To support various functions ofthe mobile device 2700, the memory 2702 can store information and data,such as instructions, software, values, images, and other data processedor referenced by the processor 2701. For example, various types ofRandom Access Memory (RAM) devices, Read Only Memory (ROM) devices,Flash Memory devices, and other suitable storage media can be used toimplement storage functions of the memory 2702. In some implementations,the mobile device 2700 includes an input/output (I/O) unit 2703 tointerface the processor 2701 and/or memory 2702 to other modules, unitsor devices. For example, the I/O unit 2703 can interface the processor2701 and memory 2702 with to utilize various types of wirelessinterfaces compatible with typical data communication standards, e.g.,such as between the one or more computers in the cloud and the userdevice. In some implementations, the mobile device 2700 can interfacewith other devices using a wired connection via the I/O unit 2703. Themobile device 2700 can also interface with other external interfaces,such as data storage, and/or visual or audio display devices 2704, toretrieve and transfer data and information that can be processed by theprocessor, stored in the memory, or exhibited on an output unit of adisplay device 2704 or an external device. For example, the displaydevice 2704 can display a video frame modified based on the MVPs inaccordance with the disclosed technology.

FIG. 29 is another example of a block diagram of a video processingsystem in which disclosed techniques may be implemented. FIG. 29 is ablock diagram showing an example video processing system 2900 in whichvarious techniques disclosed herein may be implemented. Variousimplementations may include some or all of the components of the system2900. The system 2900 may include input 2902 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 2902 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as wirelessfidelity (Wi-Fi) or cellular interfaces.

The system 2900 may include a coding component 2904 that may implementthe various coding or encoding methods described in the presentdisclosure. The coding component 2904 may reduce the average bitrate ofvideo from the input 2902 to the output of the coding component 2904 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 2904 may be eitherstored, or transmitted via a communication connected, as represented bythe component 2906. The stored or communicated bitstream (or coded)representation of the video received at the input 2902 may be used bythe component 2908 for generating pixel values or displayable video thatis sent to a display interface 2910. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include serial advanced technology attachment (SATA),peripheral component interconnect (PCI), integrated drive electronics(IDE) interface, and the like. The techniques described in the presentdisclosure may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

In some embodiments, the video coding methods may be implemented usingan apparatus that is implemented on a hardware platform as describedwith respect to FIG. 39, 40 or 40B.

FIG. 41A is a flowchart representation of an example method for videoprocessing. The method 4100 includes, at step 4102, determining, basedon a position rule, whether a local illumination compensation (LIC) toolis enabled for a conversion between a current block in a video region ofa video and a coded representation of the video. The method 4100 furtherincludes, at step 4104, performing the conversion based on the positionrule. In some implementations, the position rule specifies that the LICtool is enabled for blocks on boundaries of the video region anddisabled for blocks inside the video region and the LIC tool includesusing a linear model of illumination changes in the current block duringthe conversion.

FIG. 41B is a flowchart representation of an example method for videoprocessing. The method 4200 includes, at step 4202, determining, aprocedure for deriving local illumination compensation parameters usedfor a conversion between a current video block of a video region or avideo and a coded representation of the video based on a position ruleof the current video block in the video region. The method 4200 furtherincludes, at step 4204, performing the conversion based on thedetermining.

FIG. 41C is a flowchart representation of an example method for videoprocessing. The method 4300 includes, at step 4302, determining, for aconversion between a current block in a video region of a video and acoded representation of the video, local illumination compensation (LIC)parameters for a LIC operation using at least some samples ofneighboring blocks of the current block. The method 4300 furtherincludes, at step 4304, performing the conversion using the determinedLIC parameters. The LIC operation includes using a linear model ofillumination changes in the current block during the conversion.

FIG. 41D is a flowchart representation of an example method for videoprocessing. The method 4400 includes, at step 4402, performing aconversion between a current block in a video region of a video and acoded representation of the video, wherein the video is represented asvideo frames comprising video blocks, and a local illuminationcompensation (LIC) tool is enabled for video blocks that use a geometricprediction structure including a triangular prediction mode. The LICtool includes using a linear model of illumination changes in thecurrent block during the conversion.

FIG. 41E is a flowchart representation of an example method for videoprocessing. The method 4500 includes, at step 4502, performing aconversion between a current block in a video region of a video and acoded representation of the video, wherein the video is represented asvideo frames comprising video blocks, and a local illuminationcompensation (LIC) operation is performed for less than all pixels ofthe current block. The LIC operation includes using a linear model ofillumination changes in the current block during the conversion.

FIG. 41F is a flowchart representation of an example method for videoprocessing. The method 4600 includes, at step 4602, determining that alocal illumination compensation (LIC) operation is to be performed. Themethod 4600 further includes, at step 4604, dividing a current blockinto video processing data units (VPDUs) based on the determination thatthe LIC operation is to be performed. The method 4600 further includes,at step 4606, performing the LIC operation in sequence or in parallelfor the VPDUs. The LIC operation includes using a linear model ofillumination changes in the current block during the conversion.

FIG. 41G is a flowchart representation of an example method for videoprocessing. The method 4700 includes, at step 4702, determining to use arule that specifies that at most a single coding tool from a set ofcoding tools is used for a conversion between a current block of a videocomprising multiple pictures and a coded representation of the video.The method 4700 further includes, at step 4704, performing theconversion based on the rule. In some implementations, the set of codingtools includes coding tools that modify a reconstructed block of thecurrent block generated from motion information from the codedrepresentation or an inter prediction signal generated for the currentblock during the conversion.

FIG. 41H is a flowchart representation of an example method for videoprocessing. The method 4800 includes, at step 4802, determining, for aconversion between a current block of a video and a coded representationof the video, that both local illumination compensation (LIC) andcombined inter-intra prediction (CIIP) coding tools are enabled for theconversion of the current block. The method 4800 further includes, atstep 4804, performing the conversion based on the determining.

Various techniques and embodiments preferred by some embodiments may bedescribed using the following clause-based format.

Some embodiments of the disclosed technology include making a decisionor determination to enable a video processing tool or mode. In anexample, when the video processing tool or mode is enabled, the encoderwill use or implement the tool or mode in the processing of a block ofvideo, but may not necessarily modify the resulting bitstream based onthe usage of the tool or mode. That is, a conversion from the block ofvideo to the bitstream representation of the video will use the videoprocessing tool or mode when it is enabled based on the decision ordetermination. In another example, when the video processing tool ormode is enabled, the decoder will process the bitstream with theknowledge that the bitstream has been modified based on the videoprocessing tool or mode. That is, a conversion from the bitstreamrepresentation of the video to the block of video will be performedusing the video processing tool or mode that was enabled based on thedecision or determination.

Some embodiments of the disclosed technology include making a decisionor determination to disable a video processing tool or mode. In anexample, when the video processing tool or mode is disabled, the encoderwill not use the tool or mode in the conversion of the block of video tothe bitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was enabled based on thedecision or determination.

The first set of clauses describe certain features and aspects of thedisclosed techniques listed in the previous section, including, forexample, items 1, 2, 10, and 12-16.

1. A video processing method, comprising: determining, based on aposition rule, whether a local illumination compensation (LIC) tool isenabled for a conversion between a current block in a video region of avideo and a coded representation of the video, and performing theconversion based on the position rule, wherein the position rulespecifies that the LIC tool is enabled for blocks on boundaries of thevideo region and disabled for blocks inside the video region, andwherein the LIC tool includes using a linear model of illuminationchanges in the current block during the conversion.

2. The method of clause 1, wherein the video region is a coding treeunit (CTU) in which the current block is positioned.

3. The method of clause 1, further comprising deriving parameters forLIC of the current block, wherein the deriving uses samples ofneighboring blocks depending on a position of the current block withinthe CTU.

4. The method of clause 3, wherein (1) in case that the position of thecurrent block is at a left boundary of the CTU, the deriving uses onlyleft reconstructed neighboring samples, or (2) in case that the positionof the current block is a top boundary of the CTU, the deriving usesonly above reconstructed neighboring samples, or (3) in case that theposition of the current block is at a top-left corner of the CTU, thederiving uses left and/or above reconstructed neighboring samples, or(4) in case that the position of the current block is at a top-rightcorner of the CTU, the deriving uses above-right and/or abovereconstructed neighboring samples, or (5) in case that the position ofthe current o block is at a bottom-left corner of the CTU, the derivinguses left and/or below-left reconstructed neighboring samples.

5. A video processing method, comprising: determining, a procedure forderiving local illumination compensation parameters used for aconversion between a current video block of a video region or a videoand a coded representation of the video based on a position rule of thecurrent video block in the video region; and performing the conversionbased on the determining.

6. The method of clause 5, wherein the procedure for deriving localillumination compensation parameters comprise deriving parametersaccording to decoded information or inheriting parameters associatedwith other video blocks.

7. The method of clause 5, wherein the position rule specifies to derivethe LIC parameters using a linear model for blocks on a boundary of thevideo region and inherit the LIC parameters for blocks inside the videoregion.

8. The method of clause 5, wherein the video region is a coding treeunit (CTU) in which the current block is positioned.

9. The method of clause 6, wherein the inheriting includes: maintaininga number of look-up tables (LUTs) of LIC parameters previously used forother blocks; and deriving LIC parameters for the current block based onone or more LIC parameters from the look-up table.

10. The method of clause 6, wherein the LUT is maintained for eachreference picture.

11. The method of clause 9 or 10, wherein the look-table is emptied andrebuilt for each CTU or a row of CTU or a slice or a tile or a tilegroup or a picture of the current block.

12. The method of clause 5, wherein, for the current block coded with anadvanced motion vector prediction (AMVP) mode or an affine inter mode,the coded representation is configured to include a syntax elementindicating which LIC parameters are used for the current block.

13. The method of clause 12, wherein the syntax element is indicative ofan index to an entry in the LUT.

14. The method of any of clauses 8 to 13, wherein multiple LUTs are usedfor the CTU.

15. The method of clause 14, wherein the performing conversion usesparameters from LTUs generated by a previously processed coding treeunit.

16. The method of clause 15, wherein at least one LUT is maintained foreach reference picture or for each reference picture list used in theconversion of the current block.

17. The method clause 1 or 5, wherein the current block uses a mergemode or affine merge mode for spatial or temporal merge candidate motionvectors, and wherein the inheriting includes inheriting one or both LICflag and LIC parameters from corresponding neighboring blocks.

18. The method of clause 17, wherein one or both the LIC flag and LICparameters are signaled, or differences between the LIC parameters andinherited parameters are signaled.

19. The method of clause 5, wherein the current block uses a merge modeor affine merge mode for spatial or temporal merge candidate motionvectors, and wherein the inheriting includes configuring a bitstreamwith one or more difference values and computing LIC flag or LICparameters based on the one or more difference values and one or both ofa neighboring block's LIC flag and LIC parameters.

20. The method of clause 1, wherein the current block is coded using anadvanced motion vector prediction (AMVP) or an affine inter mode, andwherein the parameters are derived using a least square errorminimization in which subsamples set of neighboring samples is used forerror minimization.

21. The method of clause 5, wherein the current block is coded with amerge mode, the LIC coding tool is disabled for combined merge candidateor average merge candidate.

22. The method of clause 21, wherein an LIC flag of the current block isset as true in case that a LIC flag of any of two merge candidates usedfor generating the combined merge candidate or the average mergecandidate is true.

23. The method of clause 21, wherein LIC parameters are inherited fromany of two merge candidates that use LIC and generate the combined mergecandidate or the average merge candidate.

24. The method of clause 5, wherein the current block is coded with amerge mode from a HMVP merge candidate, the LIC coding tool is disabled.

25. The method of clause 24, wherein an LIC flag of the current block isset as true in case that a LIC flag of the HMVP (History-based MVP)merge candidate is true.

26. The method of clause 24, wherein an LIC parameters are inheritedfrom the HMVP merge candidate in a case that a LIC flag of the HMVPmerge candidate is true.

27. The method of any of clauses 1-26, wherein the LIC tool is used onlywhen the current block meets a condition related to size or a slice typeor a tile type or a picture type of the current block or a type ofmotion information associated with the current block.

28. The method of clause 27, wherein the condition excludes block sizessmaller than M*H samples, where M and H are pre-specified integervalues.

29. The method of clause 28, wherein M*H is equal to 16 or 32 or 64.

30. The method of clause 27, wherein the condition specifies that thecurrent block has a width or a height that is smaller than or no largerthan X, where X is an integer.

31. The method of clause 30, wherein X=8.

32. The method of clause 27, wherein the condition specifies that thecurrent block has a width or a height that is greater than or no lessthan X, where X is an integer.

33. The method of clause 32, wherein X=8.

34. The method of clause 27, wherein the condition excludes at least oneof an affine inter mode, affine merge mode, sub-block coding tools, or aplanar motion vector prediction mode or a bi-predicted mode.

35. The method of clause 27, wherein at least one of a decoder motionvector refinement (DMVR) or bi-directional optical flow (BIO) tool isdisallowed when the LIC tool is enabled for the current block.

36. The method of clause 27, wherein the condition specifies that thecurrent block correspond to luma samples.

37. The method of clause 27, wherein the condition specifies that thecurrent block correspond to chroma samples.

38. A video processing method, comprising: determining, for a conversionbetween a current block in a video region of a video and a codedrepresentation of the video, local illumination compensation (LIC)parameters for a LIC operation using at least some samples ofneighboring blocks of the current block; and performing the conversionusing the determined LIC parameters, wherein the LIC operation includesusing a linear model of illumination changes in the current block duringthe conversion.

39. The method of clause 38, wherein the at least some samples ofneighboring block depend on code information of the current block or ashape of the current block.

40. The method of clause 39, wherein, a width of the current block isgreater than or equal to a height of the current block, and thereforeonly above neighboring pixels are used for deriving LIC parameters.

41. The method of clause 39, wherein, a width of the current block isless than a height of the current block, and only left neighboringpixels are used for deriving LIC parameters.

42. A video processing method, comprising: performing a conversionbetween a current block in a video region of a video and a codedrepresentation of the video, wherein the video is represented as videoframes comprising video blocks, and a local illumination compensation(LIC) tool is enabled for video blocks that use a geometric predictionstructure including a triangular prediction mode, wherein the LIC toolincludes using a linear model of illumination changes in the currentblock during the conversion.

43. The method of clause 42, wherein, for the current block for whichthe LIC is enabled, all prediction units share a same value of a LICflag.

44. The method of clause 42 or 43, wherein, for the current block thatis partitioned from a top-right corner to a bottom-left corner of thevideo region, a single set of LIC parameters is used for both predictionunits.

45. The method of clause 42 or 43, wherein, for the current block thatis partitioned from a top-left corner to a bottom-right corner of thevideo region, a single set of LIC parameters is used for each of theprediction units.

46. The method of clause 42 or 43, wherein, for prediction units codedin a merge mode, a LIC flag is inherited from merge candidates without asignaling.

47. The method of clause 42 or 43, wherein, for prediction unitsrespectively coded in an AMVP mode and a merge mode, a signaled LIC flagis applied to the prediction unit coded in the AMVP mode and one or bothof LIC flag and LIC parameters are inherited for the prediction unitcoded in the merge mode.

48. The method of clause 42 or 43, wherein, for prediction units codedin an AMVP mode, a LIC flag is signaled for each of the predictionunits.

49. A video processing method, comprising: performing a conversionbetween a current block in a video region of a video and a codedrepresentation of the video, wherein the video is represented as videoframes comprising video blocks, and a local illumination compensation(LIC) operation is performed for less than all pixels of the currentblock, wherein the LIC operation includes using a linear model ofillumination changes in the current block during the conversion.

50. The method of clause 49, wherein the LIC operation is performed onlyfor pixels on a boundary of the current block.

51. The method of clause 49, wherein the LIC operation is performed onlyfor pixels in a top portion of the current block.

52. The method of clause 49, wherein the LIC operation is performed onlyfor pixels in a left-side portion of the current block.

53. The method of clause 49, wherein the LIC operation is performed onlyfor pixels in a top-left portion of the current block.

54. The method of any of clauses 1-53, wherein whether to enable ordisable performing of the conversion using LIC is signaled in a sequenceparameter set (SPS), a picture parameter set (PPS), a video parameterset (VPS), a sequence header, a picture header, a slice header, a tilegroup head, or a group of coding tree units (CTUs).

55. The method of any of clauses 1-53, wherein information on how toperform the conversion using the LIC tool is signaled in a sequenceparameter set (SPS), a picture parameter set (PPS), a video parameterset (VPS), a sequence header, a picture header, a slice header, a tilegroup head, or a group of coding tree units (CTUs).

56. The method of any of clauses 1-53, wherein at least one of i)whether to enable or disable performing of the conversion or ii) whichmethod is used to perform the conversion using LIC depends on a blockdimension, a video processing data unit (VPDU), a picture type, a lowdelay check flag, or coded information of the current block orpreviously coded blocks.

57. A video processing method, comprising: determining that a localillumination compensation (LIC) operation is to be performed; dividing acurrent block into video processing data units (VPDUs) based on thedetermination that the LIC operation is to be performed; and performingthe LIC operation in sequence or in parallel for the VPDUs, wherein theLIC operation includes using a linear model of illumination changes inthe current block during the conversion.

58. The method of clause 57, wherein the performing of the LIC operationin sequence allows a LIC operation of a process-block to depend on a LICoperation of another process block.

59. The method of clause 57, wherein the performing of the LIC operationin parallel makes a LIC operation of a process-block not dependent on aLIC operation of another process block.

60. The method of any of clauses 1 to 59, wherein the performing of theconversion includes generating the coded representation from the currentblock.

61. The method of any of clauses 1 to 59, wherein the performing of theconversion includes generating the current block from the codedrepresentation.

62. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method recited in one or more of clauses 1 to 61.

63. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method recited in one or more of clauses 1 to 61.

The second set of clauses describe certain features and aspects of thedisclosed techniques listed in the previous section, including, forexample, items 3-5.

1. A video processing method, comprising: determining to use a rule thatspecifies that at most a single coding tool from a set of coding toolsis used for a conversion between a current block of a video comprisingmultiple pictures and a coded representation of the video; andperforming the conversion based on the rule, wherein the set of codingtools includes coding tools that modify a reconstructed block of thecurrent block generated from motion information from the codedrepresentation or an inter prediction signal generated for the currentblock during the conversion.

2. The method of clause 1, wherein the set of coding tools includes acombined intra-inter prediction (CIIP), a diffusion filter, a bilateralfilter, a transform domain filter, overlapped block motion compensation(OBMC), or a local illumination compensation (LIC).

3. The method of clause 2, wherein in case that the LIC is enabled, therule specifies to disable other tools than the LIC.

4. The method of clause 2, wherein in case that the CIIP is enabled, therule specifies to disable other tools than the CIIP.

5. The method of clause 2, wherein in case that the diffusion filter isenabled, the rule specifies to disable other tools than the diffusionfilter.

6. The method of clause 2, wherein in case that the overlapped blockmotion compensation is enabled, the rule specifies to disable othertools than the overlapped block motion compensation.

7. The method of clause 2, wherein in case that the bilateral filter isenabled, the rule specifies to disable other tools than the bilateralfilter.

8. The method of any of clause 2-7, wherein the coded representationexcludes any syntax element associated with one or more coding toolsthat are disabled.

9. The method of clause 2, further comprising: checking at least some ofthe CIIIP, the diffusion filter, the bilateral filter, the transformdomain filter, the OBMC, or the LIC in a certain order.

10. The method of clause 9, wherein the certain order depends on atleast one of previously coded information or the coded information ofthe current block.

11. The method of any of clauses 1-10, further comprising: determining acoded mode of neighboring blocks of the current block, or of blockswithin non-adjacent rows or columns in relation to the current block,and wherein applying or performing the LIC, CIIP, diffusion filter,bilateral filter, or transform domain filter is based on thedetermination of the coded mode.

12. The method of clause 11, wherein the video blocks withinnon-adjacent rows are above or above-right rows in relation to a row ofthe video block.

13. The method of clause 11, wherein the video blocks withinnon-adjacent columns are left or below-left columns in relation to acolumn of the video block.

14. The method of clause 11, wherein the coded mode includes one or bothof intra mode or combined intra-inter mode (CIIP).

15. The method of clause 11, wherein the coded mode is not intra orCIIP.

16. The method of clause 11, wherein applying or performing includesshort-tap filters, fewer neighboring samples to be utilized for LICparameter derivation, or padding of reference samples.

17. The method of any of clauses 1-10, further comprising: determining acoded mode of neighboring video blocks of the current block, or of videoblocks within non-adjacent rows or columns in relation to the currentblock, and wherein applying or performing the LIC, CIIP, diffusionfilter, bilateral filter, or transform domain filter is disabled basedon the determination of the coded mode.

18. The method of clause 17, wherein the neighboring blocks include oneor more of: (1) an above neighboring or non-adjacent above neighboringvideo block in a neighboring or non-adjacent row is intra coded orcombined intra-inter mode coded, (2) a left neighboring or non-adjacentleft neighboring video block in a neighboring or non-adjacent column isintra coded or combined intra-inter mode coded, or (3) all blocks in theneighboring or non-adjacent row or column is intra coded or combinedintra-inter mode coded.

19. The method of clause 17, wherein the video block is LIC coded, andneighboring samples coded with intra mode or combined intra-inter modeare excluded from derivation of LIC parameters.

20. The method of clause 17, wherein neighboring samples coded withnon-intra mode or non-CIIP mode are included for derivation of LICparameters.

21. The method of clause 17, wherein one or both of short-tap filteringor padding of reference samples are applied based on the LIC, CIIP,diffusion filter, bilateral filter, or transform domain filter beingdisabled.

22. The method of clause 17, wherein video blocks within neighboringrows or columns in relation to the current block or video blocks withinnon-adjacent rows or columns in relation to the current block in areference picture are used as a replacement of the current block'sneighboring row or column or non-adjacent row or column.

23. A method for video processing, comprising: determining, for aconversion between a current block of a video and a coded representationof the video, that both local illumination compensation (LIC) andcombined inter-intra prediction (CIIP) coding tools are enabled for theconversion of the current block; and performing the conversion based onthe determining.

24. The method of clause 23, wherein information associated with theCIIP coding tool is signaled after information associated with the LICcoding tool.

25. The method of clause 23, wherein information associated with the LICcoding tool is signaled after information associated with the CIIPcoding tool.

26. The method of clause 24 or 25, wherein the information is signaledin a sequence parameter set (SPS), a picture parameter set (PPS), aslice header, a tile group header, a tile, a coding unit (CU) or acoding tree unit (CTU).

27. The method of clause 23, wherein an LIC flag is true, and whereinthe coded representation excludes one or more syntax elements associatedwith the CIIP coding tool.

28. The method of clause 27, wherein the CIIP coding tool is disabled.

29. The method of clause 23, wherein a CIIP flag is true, and whereinthe coded representation excludes one or more syntax elements associatedwith the LIC coding tool.

30. The method of clause 29, wherein LIC is disabled.

31. The method of clause 23, wherein a CIIP is enabled, and wherein thecoded representation excludes one or more syntax elements associatedwith the LIC coding tool.

32. The method of any of clauses 1 to 31, wherein the performing of theconversion includes generating the coded representation from the currentblock.

33. The method of any of clauses 1 to 32, wherein the performing of theconversion includes generating the current block from the codedrepresentation.

34. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method recited in one or more of clauses 1 to 33.

35. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method recited in one or more of clauses 1 to 33.

The disclosed and other embodiments, modules and the functionaloperations described in this disclosure can be implemented in digitalelectronic circuitry, or in computer software, firmware, or hardware,including the structures disclosed in this disclosure and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for execution by, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this disclosure can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., a field programmable gate array (FPGA) or anapplication specific integrated circuit (ASIC).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., erasable programmable read-onlymemory (EPROM), electrically erasable programmable read-only memory(EEPROM), and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto optical disks; and compact disc,read-only memory (CD ROM) and digital versatile disc read-only memory(DVD-ROM) disks. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

While the present disclosure contains many specifics, these should notbe construed as limitations on the scope of any embodiment or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular disclosures. Certainfeatures that are described in the present disclosure in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in the present disclosure should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in the present disclosure.

What is claimed is:
 1. A video processing method, comprising:determining to use a rule that specifies that at most a single codingtool from a set of coding tools is used for a conversion between acurrent block of a video comprising multiple pictures and a codedrepresentation of the video; and performing the conversion based on therule, wherein the set of coding tools includes coding tools that modifya reconstructed block of the current block generated from motioninformation from the coded representation or an inter prediction signalgenerated for the current block during the conversion, wherein the setof coding tools includes a combined intra-inter prediction (CIIP), adiffusion filter, a bilateral filter, a transform domain filter,overlapped block motion compensation (OBMC), or a local illuminationcompensation (LIC).
 2. The method of claim 1, wherein the LIC is enabledfor video blocks that use a geometric prediction structure including atriangular prediction mode.
 3. The method of claim 1, wherein the LIC isenabled for video blocks that use a multi-hypothesis prediction tool. 4.The method of claim 1, further comprising: checking at least some of theCIIIP, the diffusion filter, the bilateral filter, the transform domainfilter, the OBMC, or the LIC in a certain order, wherein the certainorder depends on at least one of previously coded information or codedinformation of the current block.
 5. The method of claim 1, furthercomprising: determining a coded mode of neighboring blocks of thecurrent block, or of blocks within non-adjacent rows or columns inrelation to the current block, and wherein applying or performing theLIC, the CIIP, the diffusion filter, the bilateral filter, or thetransform domain filter is based on the determination of the coded mode.6. The method of claim 5, wherein video blocks within the non-adjacentrows are above or above-right rows in relation to a row of a videoblock.
 7. The method of claim 5, wherein video blocks withinnon-adjacent columns are left or below-left columns in relation to acolumn of a video block.
 8. The method of claim 5, wherein the codedmode includes one or both of intra mode or combined intra-inter mode(CIIP).
 9. The method of claim 5, wherein the coded mode is not intra orCIIP.
 10. The method of claim 5, wherein applying or performing includesshort-tap filters, fewer neighboring samples to be utilized for LICparameter derivation, or padding of reference samples.
 11. The method ofclaim 1, further comprising: determining a coded mode of neighboringvideo blocks of the current block, or of video blocks withinnon-adjacent rows or columns in relation to the current block, andwherein applying or performing the LIC, the CIIP, the diffusion filter,the bilateral filter, or the transform domain filter is disabled basedon the determination of the coded mode.
 12. The method of claim 11,wherein the neighboring video blocks include one or more of: (1) anabove neighboring or non-adjacent above neighboring video block in aneighboring or non-adjacent row is intra coded or combined intra-intermode coded, (2) a left neighboring or non-adjacent left neighboringvideo block in a neighboring or non-adjacent column is intra coded orcombined intra-inter mode coded, or (3) all blocks in the neighboring ornon-adjacent row or column is intra coded or combined intra-inter modecoded.
 13. The method of claim 11, wherein the video blocks are LICcoded, and neighboring samples coded with intra mode or combinedintra-inter mode are excluded from derivation of LIC parameters.
 14. Themethod of claim 11, wherein neighboring samples coded with non-intramode or non-CIIP mode are included for derivation of LIC parameters. 15.The method of claim 11, wherein one or both of short-tap filtering orpadding of reference samples are applied based on the LIC, the CIIP, thediffusion filter, the bilateral filter, or the transform domain filterbeing disabled.
 16. The method of claim 11, wherein video blocks withinneighboring rows or columns in relation to the current block or videoblocks within the non-adjacent rows or columns in relation to thecurrent block in a reference picture are used as a replacement of thecurrent block's neighboring row or column or non-adjacent row or column.17. The method of claim 1, wherein the performing of the conversionincludes generating the coded representation from the current block. 18.The method of claim 1, wherein the performing of the conversion includesgenerating the current block from the coded representation.
 19. Anapparatus in a video system comprising a processor and a non-transitorymemory with instructions thereon, wherein the instructions uponexecution by the processor, cause the processor to: determine to use arule that specifies that at most a single coding tool from a set ofcoding tools is used for a conversion between a current block of a videocomprising multiple pictures and a coded representation of the video;and perform the conversion based on the rule, wherein the set of codingtools includes coding tools that modify a reconstructed block of thecurrent block generated from motion information from the codedrepresentation or an inter prediction signal generated for the currentblock during the conversion, wherein the set of coding tools includes acombined intra-inter prediction (CIIP), a diffusion filter, a bilateralfilter, a transform domain filter, overlapped block motion compensation(OBMC), or a local illumination compensation (LIC).
 20. A non-transitorycomputer-readable recording medium storing a bitstream of a video whichis generated by a method performed by a video processing apparatus,wherein the method comprises: determining to use a rule that specifiesthat at most a single coding tool from a set of coding tools is used fora conversion between a current block of the video comprising multiplepictures and a coded representation of the video; and generating thebitstream based on the rule, wherein the set of coding tools includescoding tools that modify a reconstructed block of the current blockgenerated from motion information from the coded representation or aninter prediction signal generated for the current block during theconversion, wherein the set of coding tools includes a combinedintra-inter prediction (CIIP), a diffusion filter, a bilateral filter, atransform domain filter, overlapped block motion compensation (OBMC), ora local illumination compensation (LIC).